(3)
  (2)    ()
()  ()

(3)
  (2)    (4)
()  ()  () ()

#lang racket

(define (left tree)
  (list-ref tree 0)
  )
(define (value tree)
  (list-ref tree 1)
  )
(define (right tree)
  (list-ref tree 2)
  )
(define (merge left value right)
  (append (cons left '()) (append (cons value '()) (cons right '())))
  )
(define (insert tree n)
  (cond
    [(empty? tree) (append '(()) (cons n '()) '(()))] ; leaf
    [(> (value tree) n) (merge (insert (left tree) n) (value tree)(right tree))] ; internal - go left
    [(< (value tree) n) (merge (left tree) (value tree) (insert (right tree) n))] ; internal - go right
    [(eq? (value tree) n) tree] ; internal - n already in tree
    )
  )