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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 __remove_child(self, parent_tree_node, index):
 """ Called from the root tree node when a node is removed from the tree. This method removes it into the item model controller. """

        # get parent and item
        parent_item = self.__mapping[id(parent_tree_node)]
        # manage the item model
        self.item_model_controller.begin_remove(index, index, parent_item.row, parent_item.id)
        child_item = parent_item.children[index]
        parent_item.remove_child(child_item)
        self.__mapping.pop(id(child_item.data["tree_node"]))
        self.item_model_controller.end_remove()