'Olive tree' in the Bible

And if some of the branches were broken off, and you, being a wild olive tree, were grafted in among them, and with them partake of the root and fatness of the olive tree;

For if you were cut out of the olive tree which is wild by nature, and were grafted contrary to nature into a good olive tree: how much more shall these, who are the natural branches, be grafted into their own olive tree?