Binary Tree

The simplest form of tree is a binary tree. A binary tree consists of  maximum two child nodes,
a.    a node (called the root node) and
b.    left and right sub-trees.
Both the sub-trees are themselves binary trees.

The nodes at the lowest levels of the tree (the ones with no sub-trees) are called leaves.

In an ordered binary tree,
1.    the keys of all the nodes in the left sub-tree are less than that of the root,
2.    the keys of all the nodes in the right sub-tree are greater than that of the root,
3.    the left and right sub-trees are themselves ordered binary trees.