In this exercise, the Tree node is shown as having links down the Tree. Is it possible for the Tree node to have links to the parent?
In most cases, the nodes used in Tree data structures only have links to child nodes. There are some variations of the general Tree data structure which do utilize nodes that have links to the parents. One example of this is the Splay Tree which is a self-adjusting binary tree. The nodes in a Splay Tree contain links to the parent nodes.