Just because. (http://myui.hateblo.jp/entry/2015/10/06/Treasure_Data_Summer_Intern_2015)

draw_binarytree.py

def padding(char, num, padc='_'):
    padcs = padc * num
    return padcs + char + padcs

def draw(stack, n, i):
    if n < 1:
        return stack

    num = 2 ** (n - 1)
    char = str(num)
    pad_num = 2 ** i - 1
    unit = padding(char, pad_num)
    line = '_'.join([unit] * num)
    stack.append(line)
    return draw(stack, n-1, i+1)

for x in reversed(draw([], 4, 0)):
    print(x)