Some LeetCode questions such as [this one](https://leetcode.com/problems/cousins-in-binary-tree/) use a binary tree with null pointers like this:\n\n``` [3,9,20,null,null,15,7]```\n\nto create a tree that looks like this:\n\n```     \n    3\n   / \\\n  9  20\n    /  \\\n   15   7\n   ```\nMy own implementation of a Binary Tree (in JavaScript) works unless I try to add null as node values in an attempt to create trees with the same structure as the examples. I have searched unsuccessfully for examples of how to implement this. Can someone help me to write a Binary Tree add method which accounts for nulls in this way?

Some LeetCode questions such as this one use a binary tree with null pointers like this:\n\n[3,9,20,null,null,15,7]\n\nto create a tree that looks like this:\n\