'Mulberry trees' in the Bible

And David inquired of Jehovah; and he said, Thou shalt not go up; turn round behind them and come upon them opposite the mulberry-trees.

And it shall be, when thou hearest a sound of marching in the tops of the mulberry-trees, that then thou shalt bestir thyself; for then will Jehovah have gone forth before thee, to smite the army of the Philistines.