Check if all leaves are at same level

//User function Template for Java

/* A Binary Tree node
class Node
{
    int data;
    Node left, right;

    Node(int item)
    {
        data = item;
        left = right = null;
    }
}
*/

class Solution
{
    
    
    public boolean check(Node root)
    {
	// Your code here
	
	
	    HashSet<Integer> result = new HashSet<>();
	    dfs(root, 0, result);
	    return result.size() == 1;
	
	
	
	
	
    }
    
    public void dfs(Node node, int i, HashSet<Integer> result)
    {
        
        
        if(node == null)
        {
            return;
            
        }
        
        dfs(node.left, i+1, result);
        dfs(node.right, i+1, result);
        
        
        if(node.left == null && node.right == null)
        {
            result.add(i);
            
        }
        
        
        
    }
}