Check for Balanced BST

You are given the root of a binary search tree (BST). Your task is to determine if the tree is height-balanced. A height-balanced tree is defined as a tree where the left and right subtrees of every node differ in height by no more than one. Implement the function `is_balanced(root)` that returns True if the tree is balanced, and False otherwise. Input format: The first line contains an integer N, the number of nodes in the BST. The following N lines each contain an integer representing the value of the node. Output format: Boolean value (True or False) based on whether the BST is height-balanced. Example: Input: 5 3 9 20 15 7 Output: True