(define my-tree (make-nonempty-tree 4
(make-leaf 2)
(make-leaf 6)))
⇒ (4 (2 () ()) (6 () ()))
Suppose we had a procedure called insert that inserts an integer as a
leaf into the appropriate place in a BST:
(insert 3 my-tree)
⇒ (4 (2 () (3 () ())) (6 () ()))
