Brother tree

Brother tree --- братское дерево, HB-дерево.

A brother tree is a rooted oriented tree each of whose internal nodes has either one or two sons. Each unary node must have a binary brother. All external nodes are at the same depth. The number of internal binary nodes of a brother tree is called its size. Note that the number of external nodes of a brother tree is always by 1 greater than its size.

Another name is HB-Tree.