1. BST/AVL Tree (25 pts:15+10) a) A BST is an AVL tree if for every node, the difference in the heights of its children is at most one. (The height of an empty tree is -1.) Here's the BSTNode definition. public clasa BSTNode C T data; BSTNode left, right; int height; Complete the following RECURSIVE implementation to check if a BST is an AVL tree, assuming the height field of each node has been already filled (You can use the Math.abe(iat 1) method to get the absolute value of an integer.) You may NOT use helper methods // Recursive implementation to check is a BST is an AVL tree public static boolean isAVL (BSTNodecT> root) f /COMPLETE THIS METHOD. (Math.ahs(voot-le theigh-aat .,git.hei nr)> 1) nhin trhei + 3 re hom is(toot 'tebr), t3