A 2-3 tree is a balanced search tree where each node can have either two children and one value (2-node), or three children and two values (3-node). For more information see http://scienceblogs.com/goodmath/2009/03/two-three_trees_a_different_ap.php and http://cs.wellesley.edu/~cs230/spring07/2-3-trees.pdf.

I implemented a 2-3 tree with no any purpose, however a 2-3 tree implements Java Set interface, and partially implements SortedSet interface.