(define (BST t level)
  (cond
    [(empty? (second t)) ""]
    [else (BST (second t) (+ 1 level))]
  )
      (display (~a (first t)  #:min-width (* 4 level) #:align 'center))
    (newline)

  (cond
    [(empty? (third t)) ""]
    [else (BST (third t) (+ 1 level))]
  )
)



(BST '(1 (0 () ()) (10 (5 () ()) (17 (12 () ()) (20 (19 () ()) ())))) 0)