'Olive tree' in the Bible

And if some of the branches have been pruned away, and you, although you were but a wild olive, have been grafted in among them and have become a sharer with others in the rich sap of the root of the olive tree,

and if you were cut from that which by nature is a wild olive and contrary to nature were grafted into the good olive tree, how much more certainly will these natural branches be grafted on their own olive tree?