The Free On-line Dictionary of Computing (30 December 2018):

binary tree

   (btree) A tree in which each node has at most two successors
   or child nodes.  In Haskell this could be represented as

   	data BTree a = NilTree
   		     | Node a (BTree a) (BTree a)

   See also balanced tree.

   (1994-11-29)