An XML tree structure allows context relationships between elements in an XML document to be expressed to any level of complexity.

A tree structure is a type of data structure in which each element is attached to one or more elements directly beneath it. The connections between elements are called branches. Trees are often called inverted trees because they are normally drawn with the root at the top.

The elements at the very bottom of an inverted tree (that is, those that have no elements below them) are called leaves. Inverted trees are the data structures used to represent hierarchical file structures. In this case, the leaves are files and the other elements above the leaves are directories.

A binary tree is a special type of inverted tree in which each element has only two branches below it.