'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 became a sharer of the root and the fatness of the olive tree with them,

For if you were cut out of the natural wild olive tree, and were grafted contrary to nature into a good olive tree; how much more these being according to nature will be grafted into their own olive-tree?