Write a method called depthSum that returns the sum of the values stored in a binary tree of integers weighted by the depth of each value. The method should return the value at the root, plus 2 times the values stored at the next level of the tree, plus 3 times the values stored at the next level of the tree, and so on. For example, the depth sum of reference tree #1 would be computed as (1 * 3) + (2 * (5 + 2)) + (3 * (1 + 4 + 6)) = 50.

Reference Tree #2 2 Reference Tree #1 1 7. 4 4 Reference Tree #3 2 3 8. 9. 3. 1.