TreeCases

TreeCases[tree, pattern] gives a list of subtrees of tree with data matching pattern.

• TreeCases[tree, pattern, levelspec] gives a list of all subtrees on levels specified by levelspec with data matching the pattern.
• TreeCases[tree, pattern, levelspec, n] gives the first n subtrees with data that matches the pattern.
• TreeCases[pattern] represents an operator form that can be applied to a tree.

Examples

tree = Tree[a, {Tree[b, {c, d}], Tree[e, {f}]}];
TreeCases[tree, _Symbol]

TreeCases[tree, b | e]

TreeCases[tree, _, 2]

*See the official Wolfram Language Reference for more details.