What is a Binary Search Tree (BST)?
A binary search tree B is a binary tree every node of which satisfies the three conditions:
1. The value of the left-subtree of 'x' is less than the value at 'x'
2. The value of the right-subtree of 'x' is greater than value at 'x'
3. the left-subtree and right-subtree of binary search tree are again binary search tree.