Parent pointer tree

In computer science, an in-tree or parent pointer tree is an N-ary tree data structure in which each node has a pointer to its parent node, but no pointers to child nodes. When used to implement a set of stacks, the structure is called a spaghetti stack, cactus stack or saguaro stack (after the saguaro, a kind of cactus). Parent pointer trees are also used as disjoint-set data structures.