A tree is called AVL (height balance binary tree), if each node possesses one of the following properties:
- A node is called left heavy if the longest path in its left sub tree is one longer then the longest path of its right sub tree.
- A node is called right heavy if the longest path in the right sub tree is one longer than path in its left sub tree.
- A node is called balanced, if the longest path in both the right and left sub tree are equal.
