code(Tree, Character, Res) :-
    code2(Tree, Character, Res),
    atomic(Character).
code2(tree(Character, _), Character, [0]).
code2(tree(_, Character), Character, [1]).
code2(tree(L, _), Character, [0|Res]) :-
    code2(L, Character, Res).
code2(tree(_, R), Character, [1|Res]) :-
    code2(R, Character, Res).