If growing apple trees isn’t hard and is no real contribution, then why do we need UBI? Everyone can just do the easy, low effort thing and grow their own apple trees and have infinite apples per their own personal UBI.

Your premise for excusing UBI contradicts the very premise for why you suspect UBI is necessary.

What you are really asking it why don’t people just do what we subjectively think they ought to instead of what they value for their own lives and what they want to do with their own time and resources? In other words, you are claiming they ought to be a slave to others before they get the right to own themselves. If your plan requires enslaving people “just a little bit,” it’s probably a bad plan that will never work.

Anything we believe someone else “should do” we must apply to ourselves first before we start thinking we can control someone else’s life better than they can.