It has a distinct node called root ie 2. And every node has either0,1 or 2 children. So it is a binary tree as every node has a maximum of 2 children.

If A is the root of a binary tree & B the root of its left or right subtree, then A is the parent or father of B and B is the left or right child of A. Those nodes having no children are leaf nodes. Any node say A is the ancestor of node B and B is the descendant of A if A is either the father of B or the father of some ancestor of B. Two nodes having same father are called brothers or siblings.

Going from leaves to root is called climbing the tree & going from root to leaves is called descending the tree.

A binary tree in which every non leaf node has non empty left & right subtrees is called a strictly binary tree. The tree shown below is a strictly binary tree.