nodes of treewe can also imagine other traversals for examplewe could traverse tree so that we visit all the nodes at depth before we visit the nodes at depth consecutively numbering the nodes of tree as we visit them in this traversal is called the level numbering of the nodes of (see section binary trees binary tree is an ordered tree with the following properties every node has at most two children each child node is labeled as being either left child or right child left child precedes right child in the ordering of children of node the subtree rooted at left or right child of an internal node is called left subtree or right subtreerespectivelyof binary tree is proper if each node has either zero or two children some people also refer to such trees as being full binary trees thusin proper binary treeevery internal node has exactly two children binary tree that is not proper is improper example an important class of binary trees arises in contexts where we wish to represent number of different outcomes that can result from answering series of yes-or-no questions each internal node is associated with question starting at the rootwe go to the left or right child of the current nodedepending on whether the answer to the question is "yesor "no with each decisionwe follow an edge from parent to childeventually tracing path in the tree from the root to an external node such binary trees are known as decision treesbecause each external node in such tree represents decision of what to do if the questions associated with ' ancestors are answered in way that leads to decision tree is proper binary tree figure illustrates decision tree that provides recommendations to prospective investor figure advice decision tree providing investment