(define (add-to-bst n s bstree)
  (cond [(= n (node-ssn bstree)) bstree]
        [(> n (node-ssn bstree)) 
         (cond [(boolean? (node-right bstree))
                (make-node
                 (node-ssn bstree)
                 (node-name bstree)
                 (node-left bstree)
                 (make-node n s false false))]
               [else (make-node
                      (node-ssn bstree)
                      (node-name bstree)
                      (node-left bstree)
                      (add-to-bst n s (node-right bstree)))])]
        [(< n (node-ssn bstree))
         (cond [(boolean? (node-left bstree))
                (make-node
                 (node-ssn bstree)
                 (node-name bstree)
                 (make-node n s false false)
                 (node-right bstree))]
               [else (make-node
                      (node-ssn bstree)
                      (node-name bstree)
                      (add-to-bst n s (node-left bstree))
                      (node-right bstree))])]))