Figure 12-1 illustrates the structure of a binary tree.
Figure 12-1. A binary tree
A leaf is a node that has no children. Each node of the tree is also considered as the root of a subtree, which consists of the node and all its descendants.
An important property of a binary tree is its height. The height is the length of the longest path from the root to any leaf. A path is a succession of linked nodes that form the connection between a given pair of nodes. The length of a path is the number of nodes in the path, not counting the first node. It follows from these definitions that a tree consisting only of its root node has a height of 0, and the height of the tree in Figure 12-1 is 3.