def save(self, filename=None):
        filename = Path(filename) if filename is not None else self.filename
        with filename.open("w") as f:
            f.write(self.yaml)
def __init__(self, key):
        self.key = key
        self.prio = random.randint(0, 1000000000)
        self.size = 1
        self.left = None
        self.right = None