Bug: disbanding a parent node group makes its children node groups inaccessible in the node groups list

[tedchwang]

Describe the bug
A clear and concise description of what the bug is.
If the parent node group is disbanded, its children node groups disappear from the node groups list, although they actually still exist and can be accessed in the graph.

To Reproduce
Steps to reproduce the behavior:

1. Create a node group (this will become the child node group)
2. Create a another node group to be the parent of the previously created node group
3. Add the child node group to the parent node group. The node groups show up in the list on the left navegation panel.
4. Disband the parent node group, see the child node group disappear.

Expected behavior
The child node group should be displayed in the list at the appropriate level of hierarchy.

Screenshots
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Desktop (please complete the following information):

• OS: Windows 10
• Browser: Chrome
• Version: 86