 The vertices of a labeled tree on "n" vertices are typically given the labels 1, 2, ..., "n".A "recursive tree" is a labeled rooted tree where the vertex labels respect the tree order (i.e., if for two vertices "u" and "v", then the label of "u" is smaller than the label of "v").In a rooted tree, the "parent" of a vertex "v" is the vertex connected to "v" on the path to the root; every vertex has a unique parent except the root which has no parent.