So it's a extended binary search tree :D useless :D
New programmers who are introduced to binary search trees quickly learn that if items are inserted in certain orders, the performance of the tree degenerates into that of a glorified linked list. Many brain cells have been devoted to the task of finding efficient ways to avoid these worst cases. Many exceedingly clever solutions have been developed, but only a handful have made it into public knowledge and even fewer into common use. Of those solutions, height balanced trees are the most common, and the AVL tree is probably the oldest of the height balanced trees.