Define a B-Tree
Justas AVL trees are balanced binary search trees, B-trees are balanced M-way search trees. A B-Tree of order M is either the empty tree or it is an M-way search tree T with the following properties:
1. Every non-leaf node has a maximum of M children and minimum of M/2 keys.
2. Every node has one fewer key than the number of children with a maximum of M-1 keys.
3. Keys are arranged in a described order within the node. All keys in the subtree to the left of a key are predecessor of the key and that on the right are successors of the key.
4. All leaves are on the similar level.