TreeLevel

TreeLevel[tree, levelspec] gives a list of all subtrees of tree on levels specified by levelspec.

• TreeLevel[tree, levelspec -> elem] gives a list of the element elem of subtrees on levels specified by levelspec.
• TreeLevel[levelspec] represents an operator form of TreeLevel that can be applied to a tree.

Examples

tree = Tree[a, {Tree[b, {c, d}], Tree[e, {f}]}];
TreeLevel[tree, {2}]

Please visit the official Wolfram Language Reference for more details.