Implement the computeoplvalue operator rvalue helper method

Question

1. Implement the function treeSize(root), which computes the number of nodes in a binary tree.

2. Implement the function treeHeight(root), which computes the height of a binary tree.

3. Implement the computeOp(lvalue, operator, rvalue) helper method used to compute the value of a binary operator when evaluating an expression tree. Assume all operands in the expression tree are single digits.