Trees-4 Problem1 Kth Smallest Element in a BST (https://leetcode.com/problems/kth-smallest-element-in-a-bst/description/) Problem2 Lowest Common Ancestor of a Binary Search Tree (https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/) Problem3 Lowest Common Ancestor of a Binary Tree (https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/)