decision_tree_nl

from itertools import combinations

def dec_tree(digit):
    res = [tuple(x for x in range(digit))]
    while len(min(res)) != 1:
        new_list = []
        for item in res:
            new_list.extend(combinations(item, len(min(res)) - 1))
        res.extend(new_list)
    return sorted([list(x) for x in set(sorted(res))])

assert dec_tree(2) == sorted([[0], [1], [0,1]])
assert dec_tree(3) == sorted([[0], [1], [2], [0,1], [0,2], [1,2], [0,1,2]])
assert dec_tree(4) == sorted(
    [[0], [1], [2], [3], [0, 1], [0, 2], [0, 3], [1, 2],
    [1, 3], [2, 3], [0, 1, 2], [0, 1, 3], [0, 2, 3], [1, 2, 3], [0, 1, 2, 3]])