A tree defining the syntactic structure of a sentence in a context-free language. The interior nodes are labelled by nonterminals of the context-free grammar; the descendants of a node labelled by A, say, spell from left to right the right-hand side of some production having left-hand side A. The leaf nodes of a parse tree may be terminals or nonterminals. If all the leaves are terminals then they spell from left to right a sentence of the language.

An example of a parse tree is shown in the diagram. It is assumed that the grammar in question has productions

Note that it is conventional for the top of the tree to be its root and the bottom to be its leaves.

An early stage in compiling a program usually consists of generating a parse tree in which the constructs that make up the program are expressed in terms of the syntax of the programming language.