Whatever Nathanael was doing under the fig tree, it was a moment of truth for him, a moment when he demonstrated his integrity. Had he refused a shady deal at the city gates? Was he in contrite, humble prayer in his backyard? Wherever he was, whatever he was doing under that fig tree, Jesus knew it and used it to show him that of such are the kingdom of God.
This is my choice of tree.
Read it at the end of John 1.