Adelson-Velsky and Landis (AVL) Tree

Definition

The BST tree when converted to a height balanced tree then it becomes an AVL Tree. Balancing factor of a tree node is the difference between the heights of the left and right sub tree.

For a tree to be height-balanced the factor should belong to a value in the set $\{1, 0, -1\}$. More specifically the absolute difference of heights of right and left subtree must be either $0$ or $1$.

graph TD;
    A[30] -->|BF = 1 - 1 = 0| B[20]
    A -->|BF = 1 - 0 = 1| C[40]
    B -->|BF=0| D[10]
    B -->|BF=0| E[25]
    C -->|BF=0| F[50]

Inserting in AVL