Binary tree is an important class of tree in data structure. A node in binary tree can have at most two children, which are called sub-trees. Children of a node in binary tree are ordered. One child is called left child and another child is called right child.

A binary tree can be defined as

- an empty tree is a binary tree
- a binary tree consists of a node is called root, a left and right sub-tree both of which are binary trees once again.