// Convert a given tree to its Sum Tree
// Given a Binary Tree where each node has positive and negative values.
// Convert this to a tree where each node contains the sum of the left and right sub trees in the original tree.
// The values of leaf nodes are changed to 0.

// For example, the following tree

//                   10
//                /      \
//        -2        6
//            /   \      /  \
//    8     -4    7    5

// should be changed to:

//                  20(4-2+12+6)
//                /      \
//      4(8-4)      12(7+5)
//            /   \      /  \
//    0      0    0    0

// Convert a given tree to its Sum Tree
// Given a Binary Tree where each node has positive and negative values.
// Convert this to a tree where each node contains the sum of the left and right sub trees in the original tree.
// The values of leaf nodes are changed to 0.

// For example, the following tree

//                   10
//                /      \
//        -2        6
//            /   \      /  \
//    8     -4    7    5

// should be changed to:

//                  20(4-2+12+6)
//                /      \
//      4(8-4)      12(7+5)
//            /   \      /  \
//    0      0    0    0


/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */



add given data structure