Returns a set of n labels sampled from the labels of the tree
        :param n: Number of labels to sample
        :return: set of randomly sampled labels

def sample_labels(self, n):
        """ Returns a set of n labels sampled from the labels of the tree
        :param n: Number of labels to sample
        :return: set of randomly sampled labels
        """
        if n >= len(self):
            return self.labels
        sample = random.sample(self.labels, n)
        return set(sample)