Binary tree object.
operator [](): Retrieve specified key from tree.iterator: Current node in iterator.root_node: Root node of tree (do not touch!)__op_array__(): Retrieve specified key from tree.count(): Counts the number of nodes in the tree.cur(): Return current item pointed to by iterator.next(): Move iterator to next item in tree.remove(key, ): Removed specified node from tree.reset(): Reset iterator to beginning.set(key, value, ): Set specified key to specified value.