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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 get_node_sum(self, age=None):
 """Get sum of all branches in the tree. Returns: int: The sum of all nodes grown until the age. """

        if age is None:
            age = self.age

        return age if self.comp == 1 else int((pow(self.comp, age+1) - 1) / (self.comp - 1))