diff --git a/docs/.gitignore b/docs/.gitignore
index f3c3680f..f4b2a542 100644
--- a/docs/.gitignore
+++ b/docs/.gitignore
@@ -1,4 +1,7 @@
 notebook-simulation.trees
 notebook-simulation.samples
 notebook-simulation-source.trees
+notebook-simulation.vc*
+notebook-simulation-AA.npy
 P_dom_chr24_phased.samples
+sparrows.vcz
diff --git a/docs/_static/example_data.vcz/.zattrs b/docs/_static/example_data.vcz/.zattrs
new file mode 100644
index 00000000..f778611e
--- /dev/null
+++ b/docs/_static/example_data.vcz/.zattrs
@@ -0,0 +1,6 @@
+{
+    "contigs": [
+        "0"
+    ],
+    "source": "sgkit-0.9.0"
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/.zgroup b/docs/_static/example_data.vcz/.zgroup
new file mode 100644
index 00000000..3b7daf22
--- /dev/null
+++ b/docs/_static/example_data.vcz/.zgroup
@@ -0,0 +1,3 @@
+{
+    "zarr_format": 2
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/.zmetadata b/docs/_static/example_data.vcz/.zmetadata
new file mode 100644
index 00000000..24b95bd0
--- /dev/null
+++ b/docs/_static/example_data.vcz/.zmetadata
@@ -0,0 +1,243 @@
+{
+    "metadata": {
+        ".zattrs": {
+            "contigs": [
+                "0"
+            ],
+            "source": "sgkit-0.9.0"
+        },
+        ".zgroup": {
+            "zarr_format": 2
+        },
+        "call_genotype/.zarray": {
+            "chunks": [
+                8,
+                3,
+                2
+            ],
+            "compressor": {
+                "blocksize": 0,
+                "clevel": 5,
+                "cname": "lz4",
+                "id": "blosc",
+                "shuffle": 1
+            },
+            "dtype": "|i1",
+            "fill_value": null,
+            "filters": null,
+            "order": "C",
+            "shape": [
+                8,
+                3,
+                2
+            ],
+            "zarr_format": 2
+        },
+        "call_genotype/.zattrs": {
+            "_ARRAY_DIMENSIONS": [
+                "variants",
+                "samples",
+                "ploidy"
+            ],
+            "comment": "Call genotype. Encoded as allele values (0 for the reference, 1 for\nthe first allele, 2 for the second allele), -1 to indicate a\nmissing value, or -2 to indicate a non allele in mixed ploidy datasets.",
+            "mixed_ploidy": false
+        },
+        "call_genotype_mask/.zarray": {
+            "chunks": [
+                8,
+                3,
+                2
+            ],
+            "compressor": {
+                "blocksize": 0,
+                "clevel": 5,
+                "cname": "lz4",
+                "id": "blosc",
+                "shuffle": 1
+            },
+            "dtype": "|i1",
+            "fill_value": null,
+            "filters": null,
+            "order": "C",
+            "shape": [
+                8,
+                3,
+                2
+            ],
+            "zarr_format": 2
+        },
+        "call_genotype_mask/.zattrs": {
+            "_ARRAY_DIMENSIONS": [
+                "variants",
+                "samples",
+                "ploidy"
+            ],
+            "comment": "A flag for each call indicating which values are missing.",
+            "dtype": "bool"
+        },
+        "call_genotype_phased/.zarray": {
+            "chunks": [
+                8,
+                3
+            ],
+            "compressor": {
+                "blocksize": 0,
+                "clevel": 5,
+                "cname": "lz4",
+                "id": "blosc",
+                "shuffle": 1
+            },
+            "dtype": "|i1",
+            "fill_value": null,
+            "filters": null,
+            "order": "C",
+            "shape": [
+                8,
+                3
+            ],
+            "zarr_format": 2
+        },
+        "call_genotype_phased/.zattrs": {
+            "_ARRAY_DIMENSIONS": [
+                "variants",
+                "samples"
+            ],
+            "comment": "A flag for each call indicating if it is phased or not. If omitted\nall calls are unphased.",
+            "dtype": "bool"
+        },
+        "contig_id/.zarray": {
+            "chunks": [
+                1
+            ],
+            "compressor": {
+                "blocksize": 0,
+                "clevel": 5,
+                "cname": "lz4",
+                "id": "blosc",
+                "shuffle": 1
+            },
+            "dtype": "<U1",
+            "fill_value": null,
+            "filters": null,
+            "order": "C",
+            "shape": [
+                1
+            ],
+            "zarr_format": 2
+        },
+        "contig_id/.zattrs": {
+            "_ARRAY_DIMENSIONS": [
+                "contigs"
+            ],
+            "comment": "Contig identifiers."
+        },
+        "sample_id/.zarray": {
+            "chunks": [
+                3
+            ],
+            "compressor": {
+                "blocksize": 0,
+                "clevel": 5,
+                "cname": "lz4",
+                "id": "blosc",
+                "shuffle": 1
+            },
+            "dtype": "<U2",
+            "fill_value": null,
+            "filters": null,
+            "order": "C",
+            "shape": [
+                3
+            ],
+            "zarr_format": 2
+        },
+        "sample_id/.zattrs": {
+            "_ARRAY_DIMENSIONS": [
+                "samples"
+            ],
+            "comment": "The unique identifier of the sample."
+        },
+        "variant_allele/.zarray": {
+            "chunks": [
+                8,
+                2
+            ],
+            "compressor": {
+                "blocksize": 0,
+                "clevel": 5,
+                "cname": "lz4",
+                "id": "blosc",
+                "shuffle": 1
+            },
+            "dtype": "|S1",
+            "fill_value": null,
+            "filters": null,
+            "order": "C",
+            "shape": [
+                8,
+                2
+            ],
+            "zarr_format": 2
+        },
+        "variant_allele/.zattrs": {
+            "_ARRAY_DIMENSIONS": [
+                "variants",
+                "alleles"
+            ],
+            "comment": "The possible alleles for the variant."
+        },
+        "variant_contig/.zarray": {
+            "chunks": [
+                8
+            ],
+            "compressor": {
+                "blocksize": 0,
+                "clevel": 5,
+                "cname": "lz4",
+                "id": "blosc",
+                "shuffle": 1
+            },
+            "dtype": "<i8",
+            "fill_value": null,
+            "filters": null,
+            "order": "C",
+            "shape": [
+                8
+            ],
+            "zarr_format": 2
+        },
+        "variant_contig/.zattrs": {
+            "_ARRAY_DIMENSIONS": [
+                "variants"
+            ],
+            "comment": "Index corresponding to contig name for each variant. In some less common\nscenarios, this may also be equivalent to the contig names if the data\ngenerating process used contig names that were also integers."
+        },
+        "variant_position/.zarray": {
+            "chunks": [
+                8
+            ],
+            "compressor": {
+                "blocksize": 0,
+                "clevel": 5,
+                "cname": "lz4",
+                "id": "blosc",
+                "shuffle": 1
+            },
+            "dtype": "<i8",
+            "fill_value": null,
+            "filters": null,
+            "order": "C",
+            "shape": [
+                8
+            ],
+            "zarr_format": 2
+        },
+        "variant_position/.zattrs": {
+            "_ARRAY_DIMENSIONS": [
+                "variants"
+            ],
+            "comment": "The reference position of the variant."
+        }
+    },
+    "zarr_consolidated_format": 1
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/call_genotype/.zarray b/docs/_static/example_data.vcz/call_genotype/.zarray
new file mode 100644
index 00000000..105c8f40
--- /dev/null
+++ b/docs/_static/example_data.vcz/call_genotype/.zarray
@@ -0,0 +1,24 @@
+{
+    "chunks": [
+        8,
+        3,
+        2
+    ],
+    "compressor": {
+        "blocksize": 0,
+        "clevel": 5,
+        "cname": "lz4",
+        "id": "blosc",
+        "shuffle": 1
+    },
+    "dtype": "|i1",
+    "fill_value": null,
+    "filters": null,
+    "order": "C",
+    "shape": [
+        8,
+        3,
+        2
+    ],
+    "zarr_format": 2
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/call_genotype/.zattrs b/docs/_static/example_data.vcz/call_genotype/.zattrs
new file mode 100644
index 00000000..7b7753c5
--- /dev/null
+++ b/docs/_static/example_data.vcz/call_genotype/.zattrs
@@ -0,0 +1,9 @@
+{
+    "_ARRAY_DIMENSIONS": [
+        "variants",
+        "samples",
+        "ploidy"
+    ],
+    "comment": "Call genotype. Encoded as allele values (0 for the reference, 1 for\nthe first allele, 2 for the second allele), -1 to indicate a\nmissing value, or -2 to indicate a non allele in mixed ploidy datasets.",
+    "mixed_ploidy": false
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/call_genotype/0.0.0 b/docs/_static/example_data.vcz/call_genotype/0.0.0
new file mode 100644
index 00000000..23f15862
Binary files /dev/null and b/docs/_static/example_data.vcz/call_genotype/0.0.0 differ
diff --git a/docs/_static/example_data.vcz/call_genotype_mask/.zarray b/docs/_static/example_data.vcz/call_genotype_mask/.zarray
new file mode 100644
index 00000000..105c8f40
--- /dev/null
+++ b/docs/_static/example_data.vcz/call_genotype_mask/.zarray
@@ -0,0 +1,24 @@
+{
+    "chunks": [
+        8,
+        3,
+        2
+    ],
+    "compressor": {
+        "blocksize": 0,
+        "clevel": 5,
+        "cname": "lz4",
+        "id": "blosc",
+        "shuffle": 1
+    },
+    "dtype": "|i1",
+    "fill_value": null,
+    "filters": null,
+    "order": "C",
+    "shape": [
+        8,
+        3,
+        2
+    ],
+    "zarr_format": 2
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/call_genotype_mask/.zattrs b/docs/_static/example_data.vcz/call_genotype_mask/.zattrs
new file mode 100644
index 00000000..6a43b7ab
--- /dev/null
+++ b/docs/_static/example_data.vcz/call_genotype_mask/.zattrs
@@ -0,0 +1,9 @@
+{
+    "_ARRAY_DIMENSIONS": [
+        "variants",
+        "samples",
+        "ploidy"
+    ],
+    "comment": "A flag for each call indicating which values are missing.",
+    "dtype": "bool"
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/call_genotype_mask/0.0.0 b/docs/_static/example_data.vcz/call_genotype_mask/0.0.0
new file mode 100644
index 00000000..574f3547
Binary files /dev/null and b/docs/_static/example_data.vcz/call_genotype_mask/0.0.0 differ
diff --git a/docs/_static/example_data.vcz/call_genotype_phased/.zarray b/docs/_static/example_data.vcz/call_genotype_phased/.zarray
new file mode 100644
index 00000000..c862e179
--- /dev/null
+++ b/docs/_static/example_data.vcz/call_genotype_phased/.zarray
@@ -0,0 +1,22 @@
+{
+    "chunks": [
+        8,
+        3
+    ],
+    "compressor": {
+        "blocksize": 0,
+        "clevel": 5,
+        "cname": "lz4",
+        "id": "blosc",
+        "shuffle": 1
+    },
+    "dtype": "|i1",
+    "fill_value": null,
+    "filters": null,
+    "order": "C",
+    "shape": [
+        8,
+        3
+    ],
+    "zarr_format": 2
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/call_genotype_phased/.zattrs b/docs/_static/example_data.vcz/call_genotype_phased/.zattrs
new file mode 100644
index 00000000..7ae8d94f
--- /dev/null
+++ b/docs/_static/example_data.vcz/call_genotype_phased/.zattrs
@@ -0,0 +1,8 @@
+{
+    "_ARRAY_DIMENSIONS": [
+        "variants",
+        "samples"
+    ],
+    "comment": "A flag for each call indicating if it is phased or not. If omitted\nall calls are unphased.",
+    "dtype": "bool"
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/call_genotype_phased/0.0 b/docs/_static/example_data.vcz/call_genotype_phased/0.0
new file mode 100644
index 00000000..b368df0f
Binary files /dev/null and b/docs/_static/example_data.vcz/call_genotype_phased/0.0 differ
diff --git a/docs/_static/example_data.vcz/contig_id/.zarray b/docs/_static/example_data.vcz/contig_id/.zarray
new file mode 100644
index 00000000..ce072443
--- /dev/null
+++ b/docs/_static/example_data.vcz/contig_id/.zarray
@@ -0,0 +1,20 @@
+{
+    "chunks": [
+        1
+    ],
+    "compressor": {
+        "blocksize": 0,
+        "clevel": 5,
+        "cname": "lz4",
+        "id": "blosc",
+        "shuffle": 1
+    },
+    "dtype": "<U1",
+    "fill_value": null,
+    "filters": null,
+    "order": "C",
+    "shape": [
+        1
+    ],
+    "zarr_format": 2
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/contig_id/.zattrs b/docs/_static/example_data.vcz/contig_id/.zattrs
new file mode 100644
index 00000000..63b8cf86
--- /dev/null
+++ b/docs/_static/example_data.vcz/contig_id/.zattrs
@@ -0,0 +1,6 @@
+{
+    "_ARRAY_DIMENSIONS": [
+        "contigs"
+    ],
+    "comment": "Contig identifiers."
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/contig_id/0 b/docs/_static/example_data.vcz/contig_id/0
new file mode 100644
index 00000000..113105d5
Binary files /dev/null and b/docs/_static/example_data.vcz/contig_id/0 differ
diff --git a/docs/_static/example_data.vcz/sample_id/.zarray b/docs/_static/example_data.vcz/sample_id/.zarray
new file mode 100644
index 00000000..c27ef48d
--- /dev/null
+++ b/docs/_static/example_data.vcz/sample_id/.zarray
@@ -0,0 +1,20 @@
+{
+    "chunks": [
+        3
+    ],
+    "compressor": {
+        "blocksize": 0,
+        "clevel": 5,
+        "cname": "lz4",
+        "id": "blosc",
+        "shuffle": 1
+    },
+    "dtype": "<U2",
+    "fill_value": null,
+    "filters": null,
+    "order": "C",
+    "shape": [
+        3
+    ],
+    "zarr_format": 2
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/sample_id/.zattrs b/docs/_static/example_data.vcz/sample_id/.zattrs
new file mode 100644
index 00000000..801e30ed
--- /dev/null
+++ b/docs/_static/example_data.vcz/sample_id/.zattrs
@@ -0,0 +1,6 @@
+{
+    "_ARRAY_DIMENSIONS": [
+        "samples"
+    ],
+    "comment": "The unique identifier of the sample."
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/sample_id/0 b/docs/_static/example_data.vcz/sample_id/0
new file mode 100644
index 00000000..7ead0f07
Binary files /dev/null and b/docs/_static/example_data.vcz/sample_id/0 differ
diff --git a/docs/_static/example_data.vcz/variant_allele/.zarray b/docs/_static/example_data.vcz/variant_allele/.zarray
new file mode 100644
index 00000000..0ccff202
--- /dev/null
+++ b/docs/_static/example_data.vcz/variant_allele/.zarray
@@ -0,0 +1,22 @@
+{
+    "chunks": [
+        8,
+        2
+    ],
+    "compressor": {
+        "blocksize": 0,
+        "clevel": 5,
+        "cname": "lz4",
+        "id": "blosc",
+        "shuffle": 1
+    },
+    "dtype": "|S1",
+    "fill_value": null,
+    "filters": null,
+    "order": "C",
+    "shape": [
+        8,
+        2
+    ],
+    "zarr_format": 2
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/variant_allele/.zattrs b/docs/_static/example_data.vcz/variant_allele/.zattrs
new file mode 100644
index 00000000..2de87677
--- /dev/null
+++ b/docs/_static/example_data.vcz/variant_allele/.zattrs
@@ -0,0 +1,7 @@
+{
+    "_ARRAY_DIMENSIONS": [
+        "variants",
+        "alleles"
+    ],
+    "comment": "The possible alleles for the variant."
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/variant_allele/0.0 b/docs/_static/example_data.vcz/variant_allele/0.0
new file mode 100644
index 00000000..67ced593
Binary files /dev/null and b/docs/_static/example_data.vcz/variant_allele/0.0 differ
diff --git a/docs/_static/example_data.vcz/variant_contig/.zarray b/docs/_static/example_data.vcz/variant_contig/.zarray
new file mode 100644
index 00000000..bb6f54dd
--- /dev/null
+++ b/docs/_static/example_data.vcz/variant_contig/.zarray
@@ -0,0 +1,20 @@
+{
+    "chunks": [
+        8
+    ],
+    "compressor": {
+        "blocksize": 0,
+        "clevel": 5,
+        "cname": "lz4",
+        "id": "blosc",
+        "shuffle": 1
+    },
+    "dtype": "<i8",
+    "fill_value": null,
+    "filters": null,
+    "order": "C",
+    "shape": [
+        8
+    ],
+    "zarr_format": 2
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/variant_contig/.zattrs b/docs/_static/example_data.vcz/variant_contig/.zattrs
new file mode 100644
index 00000000..a22ac19d
--- /dev/null
+++ b/docs/_static/example_data.vcz/variant_contig/.zattrs
@@ -0,0 +1,6 @@
+{
+    "_ARRAY_DIMENSIONS": [
+        "variants"
+    ],
+    "comment": "Index corresponding to contig name for each variant. In some less common\nscenarios, this may also be equivalent to the contig names if the data\ngenerating process used contig names that were also integers."
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/variant_contig/0 b/docs/_static/example_data.vcz/variant_contig/0
new file mode 100644
index 00000000..72c48136
Binary files /dev/null and b/docs/_static/example_data.vcz/variant_contig/0 differ
diff --git a/docs/_static/example_data.vcz/variant_position/.zarray b/docs/_static/example_data.vcz/variant_position/.zarray
new file mode 100644
index 00000000..bb6f54dd
--- /dev/null
+++ b/docs/_static/example_data.vcz/variant_position/.zarray
@@ -0,0 +1,20 @@
+{
+    "chunks": [
+        8
+    ],
+    "compressor": {
+        "blocksize": 0,
+        "clevel": 5,
+        "cname": "lz4",
+        "id": "blosc",
+        "shuffle": 1
+    },
+    "dtype": "<i8",
+    "fill_value": null,
+    "filters": null,
+    "order": "C",
+    "shape": [
+        8
+    ],
+    "zarr_format": 2
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/variant_position/.zattrs b/docs/_static/example_data.vcz/variant_position/.zattrs
new file mode 100644
index 00000000..a9a8102f
--- /dev/null
+++ b/docs/_static/example_data.vcz/variant_position/.zattrs
@@ -0,0 +1,6 @@
+{
+    "_ARRAY_DIMENSIONS": [
+        "variants"
+    ],
+    "comment": "The reference position of the variant."
+}
\ No newline at end of file
diff --git a/docs/_static/example_data.vcz/variant_position/0 b/docs/_static/example_data.vcz/variant_position/0
new file mode 100644
index 00000000..ce6b6630
Binary files /dev/null and b/docs/_static/example_data.vcz/variant_position/0 differ
diff --git a/docs/tutorial.md b/docs/tutorial.md
index 23101b93..27bbf80a 100644
--- a/docs/tutorial.md
+++ b/docs/tutorial.md
@@ -27,26 +27,24 @@ _Tsinfer_ takes as input a [Zarr](https://zarr.readthedocs.io/) file, with phase
 [VCF Zarr](https://github.com/sgkit-dev/vcf-zarr-spec/) (.vcz) format. The standard
 route to create such a file is by conversion from a VCF file, e.g. using
 [vcf2zarr](https://sgkit-dev.github.io/bio2zarr/vcf2zarr/overview.html) as described later in this
-document. For a quick introduction, however, we will instead create an example file using
-[sgkit](https://sgkit-dev.github.io/sgkit/latest/).
+document. However, for the moment we'll just use a pre-generated dataset:
 
 
 ```{code-cell} ipython3
-import sgkit
-ds = sgkit.simulate_genotype_call_dataset(n_variant=8, n_sample=3, missing_pct=0, phased=True, seed=79)
-sgkit.save_dataset(ds, "data.vcz", mode="w")
+import zarr
+ds = zarr.load("_static/example_data.vcz")
 ```
 
-This is what that generated data looks like:
+This is what the genotypes stored in that datafile look like:
 
 ```{code-cell}
 :"tags": ["remove-input"]
 import numpy as np
-assert all(len(np.unique(a)) == len(a) for a in ds['variant_allele'].values) 
-assert any([np.sum(g.values) == 1 for g in ds['call_genotype']]) # at least one singleton
-assert any([np.sum(g.values) == 0 for g in ds['call_genotype']]) # at least one non-variable
+assert all(len(np.unique(a)) == len(a) for a in ds['variant_allele']) 
+assert any([np.sum(g) == 1 for g in ds['call_genotype']]) # at least one singleton
+assert any([np.sum(g) == 0 for g in ds['call_genotype']]) # at least one non-variable
 
-alleles = ds['variant_allele'].values.astype(str)
+alleles = ds['variant_allele'].astype(str)
 sites = np.arange(ds['call_genotype'].shape[0])
 print(" " * 22, "Site:", " ".join(str(x) for x in range(8)), "\n")
 for sample in range(ds['call_genotype'].shape[1]):
@@ -54,16 +52,20 @@ for sample in range(ds['call_genotype'].shape[1]):
         genotypes = ds['call_genotype'][:,sample, genome]
         print(
             f"Diploid sample {sample} (genome {genome}):",
-            " ".join(alleles[sites, genotypes.values])
+            " ".join(alleles[sites, genotypes])
         )
 ```
 
+### VariantData and ancestral alleles
+
 We wish to infer a genealogy that could have given rise to this data set. To run _tsinfer_
 we wrap the .vcz file in a `tsinfer.VariantData` object. This requires an 
 *ancestral allele* to be specified for each site; there are
 many methods for calculating there: details are outside the scope of this manual, but we
 have started a [discussion topic](https://github.com/tskit-dev/tsinfer/discussions/523)
-on this issue to provide some recommendations. Sometimes VCF files will contain the
+on this issue to provide some recommendations.
+
+Sometimes VCF files will contain the
 ancestral allele in the "AA" info field, in which case it will be encoded in the
 `variant_AA` field of the .vcz file. It's also possible to provide a numpy array
 of ancestral alleles, of the same length as the number of variants. Ancestral
@@ -73,17 +75,17 @@ and not used for inference (with a warning given).
 ```{code-cell}
 import tsinfer
 
-# In this example, take the REF allele (index 0) as ancestral
-ancestral_alleles = ds['variant_allele'].values[:,0].astype(str)
-# set the last site as of unknown ancestral allele
+# For this example take the REF allele (index 0) as ancestral
+ancestral_alleles = ds['variant_allele'][:,0].astype(str)
+# set the last site to an unknown ancestral allele, for this demo
 ancestral_alleles[-1] = "."
 
-vdata = tsinfer.VariantData("data.vcz", ancestral_alleles)
+vdata = tsinfer.VariantData("_static/example_data.vcz", ancestral_alleles)
 ```
 
 Here we create a new `.VariantData` object for the 3 diploid samples in our
 dataset. Each diploid sample will correspond to an *individual* in the resulting tree
-sequenece, and each of the 6 genomes will correspond to a sample node
+sequence, and each of the 6 genomes will correspond to a sample node
 (hence `ts.num_samples == 6`). 
 
 Not all sites are used for genealogical inference: this includes non-variable (fixed)
@@ -98,6 +100,8 @@ via the `exclude_positions` parameter). Note, however, that even if a site is no
 for genealogical inference, its genetic variation can still be encoded in the final
 tree sequence.
 
+### Topology inference
+
 Once we have stored our data in a `.VariantData` object, we can easily infer 
 a {ref}`tree sequence<sec_python_api_trees_and_tree_sequences>` using the Python
 API: