def _set_antecedent(self, descendants):
    """
    Set antecedent property of descendents to current branch.

    Notes
    -----

    We want the clusters to know who they are related to. An antecedent is the
    immediate parent of a cluster. So when branching set the antecedent property
    of all descendants in the current branch to the branch itself. Also set the
    antecedent value of the current branch to 'None' to indicate that it doens't
    have a parent.

    """

    for descendant in descendants:
        descendant._antecedent = self

    return self._antecedent