See :meth:`~pluginsmanager.observer.observable_list.ObservableList.insert()` method

def insert(self, index, x):
        """
        See :meth:`~pluginsmanager.observer.observable_list.ObservableList.insert()` method
        """
        self.check_insertion(x)

        self.real_list.insert(index, x)
        self._items |= {x}