'Mulberry trees' in the Bible

And when David inquired of the LORD, he said, Thou shalt not go up: but fetch a compass behind them, and come upon them over against the mulberry-trees.

And let it be, when thou hearest the sound of a going in the tops of the mulberry-trees, that then thou shalt bestir thyself: for then shall the LORD go out before thee, to smite the host of the Philistines.