def METHOD_NAME(self, user=None):
    """
    Return all private groups for this user.
    Retrieve all private groups that this user is a member of. List will
    be empty if no ``user`` provided. Groups will be sorted by name.
    :type user: :class:`~h.models.user`
    :rtype: list of :class:`h.models.group`
    """
    user_groups = self.user_groups(user)
    return [group for group in user_groups if group.type == "private"]