**Objective: **Given a binary tree, write an algorithm to count all the nodes in the tree.

**Example:**

**Approach:**

- Do postorder traversal.
- If the root is null return 0. (base case all well for the recursion)
- if the root is not null then make a recursive call to the left child and right child and add the result of these with 1 ( 1 for counting the root) and return.

**Code:**

**Output:**

Number of nodes in the given binary tree: 5