A tree structure is a way of representing the hierarchy|hierarchical nature of a structure in a graphical form. It is named a tree structure because the classic #Representing trees|representation resembles a tree, even though the chart is generally upside down compared to an actual tree, with the root at the top and the leaves at the bottom.
A tree structure is conceptual, and appears in several forms. For a discussion of tree structures in specific fields, see Tree (data structure) for computer science: insofar as it relates to graph theory, see tree (graph theory), or also tree (set theory). Other related pages are listed below.