Write the code for visiting the tree nodes using a post order traversal algorithm. Assume that the tree represents a directory system. Add to the structure representing the tree node an integer member representing the number of files in each tree node. Update the tree implementation by reinitializing the tree nodes with a particular number of files as presented in the figure below: Root USR 10 BIN 15 HOME Exams HWS 7 Projects 15 Grades 3 Drives Docs 18 Main 4 Dropbox OneDrive Use post order traversal to calculate the total number of files in the directory structure at the root node. Hint: While coding the post order traversal, you should sum the different number of files at the children nodes to come up with the total number of files when reaching the root node