It's actually a metaphor. A simile is "Fame is LIKE a fruit tree". The idea of the metaphor is that fame is more than "like" a fruit tree; Drake tells us that fame IS VIRTUALLY a fruit tree in essence. He makes a number of such comparisons in the song (eg. "Forgotten while you're here / Remembered for a while").

Hmm. Yes, I would say it is a comparison, or simile to be more technical (if I remember correctly from high school English). He is basically saying that fame is unstable or unreliable, but I personally don't see what that has to do with a fruit tree... I hope that helps :)