'Olive tree' in the Bible

Supposing that some of the branches have been broken off, and you, although you were but a wild olive, have been grafted in among the branches and have become a partaker with them of the fatness of the olive tree, do not glory over the branches;

For if you were cut out of that which is by nature a mere wild olive tree, and have been grafted, contrary to nature, into a fruitful olive tree, how much more shall these, the natural branches, be regrafted into their own olive tree?