Defining a node in binary tree

Every data structure comprises some fundamental elementary units that connect to make up that data structure. A node is the fundamental building block of a binary tree. Since a binary tree can have only two children, they can be conveniently named left and right depending on which side of the parent node they fall into when drawn on a 2D surface. 

Structure of a node

A binary tree node has three sections. It holds references to its two children in its left and right sections and the data items in the data section.