A tree is a combinatorial structure recursively defined to be {a node and a sequence of trees}.

See Symbolic method for unlabelled structures

See also the particular kind: Tree (Graph theory)

Types

• Rooted/Unrooted. Depending on whether a node is distinguished as the "root".
• n-ary, for instance binary. If each node has $n$ children.
• labelled/unlabelled
• ordered/unordered. An ordered rooted tree is called planted..

Graph-Theoretic Concepts in Computer Science: 29th International ..., Volume 29