Your "rules attorney" should also be aware that the GM has the final say. Period.
If need be, you can remind him that this is also stated as a rule in the book.
I'd say, every time, that it would depend on the player/character/setting for your campaign.
Why do they want the tree? Just to throw things around? Or because they think their character would know it?
Do YOU think your setting supports it?
If no, then make him earn it. But make sure you give them some opportunities. I have a players who want Force powers. I gave them a Sith Holocron (which they had to work their asses off for). Its now up to them to learn how to access it. Which takes research, dedication, focus, and personal time.
When they do? They can take FSE if they want.