A stack tree is a binary tree

Binary tree

In computer science, a binary tree is a tree data structure in which each node has at most two child nodes, usually distinguished as "left" and "right". Nodes with children are parent nodes, and child nodes may contain references to their parents. Outside the tree, there is often a reference to...

 where no node

Node (computer science)

A node is a record consisting of one or more fields that are links to other nodes, and a data field. The link and data fields are often implemented by pointers or references although it is also quite common for the data to be embedded directly in the node. Nodes are used to build linked, often...

 other than the root has more than one non-leaf child. As the elements of a binary tree have 2 children, this means that one points to the next node (and hence is a non-leaf child) and one points to a data element, or NULL. Hence the tree is essentially a singly linked linked list

Linked list

In computer science, a linked list is a data structure consisting of a group of nodes which together represent a sequence. Under the simplest form, each node is composed of a datum and a reference to the next node in the sequence; more complex variants add additional links...

, with data items hanging off each node.