B Tree
Unlike a binary-tree, every node of a B-tree may have a variable number of keys and children. The keys are stored in non-decreasing order. Every key has an associated child that is the root of a subtree having all nodes with keys less than or equal to the key but greater than the proceeding key. A node also has an additional rightmost child that is the root for a subtree having all keys greater than any keys in the node.