class Tree:
    def __init__(self, val, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

    def __str__(self): return "(%s %s %s)" % (self.val, self.left, self.right)

    def task(self, level):
        def getLevel(node, level):
            if node == None: return ""
            if level == 1 : return "[" + str(node.val) + "]"
            return str(getLevel(node.left, level - 1)) + str(getLevel(node.right, level - 1))

        result = "At level " + str(level) + " is: "
        return result + getLevel(self, level)


test4 = Tree(4)
test3 = Tree(3, test4, test4)
test2 = Tree(2, test3, test3)
test = Tree(1, test2, test2)
print(test.task(0))
print(test.task(1))
print(test.task(2))
print(test.task(3))
print(test.task(4))
print(test.task(5))

"""
At level 0 is:
At level 1 is: [1]
At level 2 is: [2][2]
At level 3 is: [3][3][3][3]
At level 4 is: [4][4][4][4][4][4][4][4]
At level 5 is:
"""