Short Answers Section 10.4 Tree Traversals (give me short c++ code for the below question)

15. Using the binary_tree_node from Section 10.3, write a recursive function to meet the following specification. You do not need to check the precondition.

template  int sum_all(binary_tree_node* root_ptr) // Precondition: root_ptr is the root pointer of a binary tree. // Postcondition: The return value is the sum of all the data in all the nodes. // NOTES: The return value for the empty tree is zero.