Adds a branch to a node, i.e. depth addition. The given
            node's md_nodes is set to the abranch's mdict_branch.

def node_branch(self, astr_node, abranch):
            """
            Adds a branch to a node, i.e. depth addition. The given
            node's md_nodes is set to the abranch's mdict_branch.
            """
            self.dict_branch[astr_node].node_dictBranch(abranch.dict_branch)