The term tree diagram is used in different ways in different disciplines.

• In physics, a tree diagram is an acyclic connected Feynman diagram. The word tree is used just as in graph theory. A tree diagram corresponds to the results obtained from classical physics in which the effects of quantum mechanics are ignored. One does not need to perform any integrals to calculate a tree diagram. The full result for the physical quantity must however include one-loop Feynman diagrams and also more complicated diagrams.
• In linguistics, a tree diagram is one way to visually represent the structure of a sentence. See Sentence diagramming. Another way is the traditional Reed-Kellogg sentence diagram.