It is a parable or fable spoken by Jotham meant to remind the Israelites that they were about to anoint his half brother the mass murderer Abimelech as their king.

This means they were about to go against the advice of their father Gideon the late Judge who had saved them from the Midianites but had refused Kingship as a reward, because it was his belief that only god not men should rule Israel because hereditary monarchy was inherently immoral and dangerous.

Abimelech (an adopted name meaning crown prince) was the bastard son of Gideon and half brother of the other 69 sons of Gideon. Abimelech murder all but one of his brothers Jotham and their father as well anyone appointed as a councilor over Israel.
These were the Olives, figs and vines, who refused to rule as a king, where as Abimelech not only wanted to rule but would, if not anointed, make himself emperor by force of arms.

It is not literal and is the root (pun intended) of several of Jesus' parables about Israel as an olive grove fig tree or vine that had failed their potential.