datatype bstree =
    br of bstree * int * bstree
    | lf


val tree = br (br (br (lf, 2, lf), 7, lf), 9, br (br (lf, 13, lf), 21, br (lf, 25, lf)));

(*fun toList(tree: bstree): int list (vrne seznam urejenih elementov podanega drevesa,
v seznamu naj bo prvi element min(tree), zadnji pa max(tree)
· za združevanje seznamov lahko uporabite operator @) *)

fun toList(tree: bstree): int list =
    case tree of
        br(left, i, right) => toList(left) @ [i] @ [] @ toList(right)
        | lf => []

toList(tree)