python测试tree颜色

我想完成一个function，他的要求如下

 请问代码该怎么写？

```python
class Node:
    def __init__(self, colour):
        self.colour = colour
        self.children = []

    def add_child(self, child):
        self.children.append(child)


class Colour:
    GREEN = 'G'
    RED = 'R'


class Tree:
    def __init__(self, start_node):
        self.start_node = start_node

    def is_coloured_to_depth_k(self, start_node: Node, colour: Colour, k: int) -> bool:
        if k == 0:
            return start_node.colour == colour

        if start_node.colour != colour:
            return False

        for child in start_node.children:
            if not self.is_coloured_to_depth_k(child, colour, k - 1):
                return False

        return True


# 构建示例树
start = Node(Colour.GREEN)
g1 = Node(Colour.GREEN)
g2 = Node(Colour.GREEN)
r = Node(Colour.RED)
g1.add_child(g1)
g1.add_child(r)
start.add_child(g1)
start.add_child(g2)
r.add_child(r)

# 创建树对象
tree = Tree(start)

# 执行示例测试
print(tree.is_coloured_to_depth_k(start, Colour.GREEN, 0))  # True
print(tree.is_coloured_to_depth_k(start, Colour.RED, 0))  # False
print(tree.is_coloured_to_depth_k(start, Colour.GREEN, 1))  # True
print(tree.is_coloured_to_depth_k(start, Colour.GREEN, 2))  # False

```
此代码基于你提供的信息，并且假设树是通过Node对象的层次结构表示的。你可以根据实际情况进行适当调整和扩展。