'Mulberry trees' in the Bible

And David inquired again of God; and God said to him, Go not up after them; turn round them and come upon them opposite the mulberry-trees.

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