def METHOD_NAME(self, element):
    """
    Add an element to the bag.
    >>> s = pbag([1])
    >>> s2 = s.add(1)
    >>> s3 = s.add(2)
    >>> s2
    pbag([1, 1])
    >>> s3
    pbag([1, 2])
    """
    return PBag(_add_to_counters(self._counts, element))