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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 set_root(self, depth, index):
 """Set the level\'s root of the given depth to index :param depth: the depth level :type depth: int :param index: the new root index :type index: QtCore.QModelIndex :returns: None :rtype: None :raises: None """

        if depth < len(self._levels):
            self._levels[depth].set_root(index)