datatype 'a btree = T of 'a btree * 'a btree |
         Leaf of 'a;

     infix 2 T;

     fun printTree(Leaf(x)) = print(Int.toString(x))
     |   printTree(t1 T t2) =
             (
                 print("(");
                 printTree(t1);
                 print(",");
                 printTree(t2);
                 print(")")
             );

     val t = Leaf(1) T Leaf(2) T Leaf(3);

     printTree(t);

     val t =
         Leaf(1) T (Leaf(2) T Leaf(3) T (Leaf(4) T Leaf(5)));

     printTree(t);