def dump(self, indent: int) -> str:
    res = [self.to_string(indent)]
    for c in self._children:
        res.append(c.dump((indent + 1)))
    return ''.join(res)
def dump(self, indent: int) -> str:
    res = [self.to_string(indent)]
    for c in self._children:
        res.append(c.dump((indent + 1)))
    return .join(res)