#| BEGIN (Write your solution here) |#
; My code
(define (successive-merge pairs)
    (if (= (length pairs) 1)
        (car pairs)
        (successive-merge
            (let ((left (car pairs)) (right (cadr pairs)) (rest (cddr pairs)))
                (adjoin-set (make-code-tree left right) rest)
            )
        )
    )
)
#| END |#