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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_group(self, L):
 """Add elements of L as descendants of the node. If there are several elements in L, group them in a P-node first """

        if len(L) == 1:
            self.add(L[0])
        elif len(L) >= 2:
            x = PQ_node(P_shape)
            x.add_all(L)
            self.add(x)