;; helper function that finds the rest that are less than or equal
(define (rest-less-eq x ls)
    (cond
      ((null? ls) #f)
      ((<= (car ls) x) ls)
      (else (rest-less-eq x (cdr ls)))))

;; nest the input as a tree
(define (make-tree input depth)
  (cond
   ((null? input) '())
   ((eq? input #f ) '())
   ((= depth (car input))
    (cons (car input)(make-tree(cdr input) depth)))
   ((< depth (car input))
    (cons (make-tree input (+ depth 1))
	  (make-tree (rest-less-eq depth input) depth)))
   (#t '())
   ))

(define examples
  '(()
    (1 2 4)
    (3 1 3 1)
    (1 2 3 1)
    (3 2 1 3)
    (3 3 3 1 1 3 3 3)))

(define (run-examples x)
  (if (null? x) '()
      (begin
	(display (car x))(display " -> ")
	(display (make-tree(car x) 1))(display "\n")
	(run-examples (cdr x)))))

(run-examples examples)