Source : Free On-Line Dictionary of Computing

TREET
     
        E.C. Haines, 1964.  An experimental variant of LISP1.5,
        implemented on the STRETCH computer.  Basic structure was a
        trinary tree.
     
        ["The TREET {Time-Sharing} System", H.A. Bayard et al, Proc
        2nd Symp Symb and Alg Manip, ACM (Mar 1971)].
     
        [Sammet 1969, pp.457-461].