'Olive tree' in the Bible

And if some of the branches be broken off, and thou, being a wild olive-tree, art ingrafted among them, and with them partakest of the root and fatness of the olive-tree;

For if thou wast cut out of the olive-tree which is wild by nature, and wast ingrafted contrary to nature into a good olive-tree; how much more shall these, which are the natural branches, be grafted into their own olive-tree?