My cousin and I just did this. We arrived on 11/16, which was the first day it started, and had lunch at Toothsome Chocolate Emporium. While we were browsing around, a guy behind the candy counter mentioned the tree hunt to us. We picked up a flyer and finished the hunt on Wednesday. (Didn't work on it on Sunday, so really just Monday & Tuesday.)
You can pick up a flyer for it at any of the trees you see, so don't worry about starting at any particular location. The trees are pretty cool and extremely well-themed to their locations. Dinosaur stuff on the one near Jurassic Park, aliens on the one in MIB, etc. The hardest to find was the one at "Silver Screen Collectibles" and we finally had to ask someone. (Pro tip - it's the Hello Kitty tree...which has NOTHING to do with 'silver screen' anything, but whatevs...)
You have to redeem them for your prize IN one of the parks. Glad we noticed that because we were going to 'cash in' for our prize on our departure day - which we didn't have park tickets for - and instead made sure to finish on our last park day so we could get our prize.
The trees are very cool and it was fun little hunt. I won't give away the prize, but I will say it made me smile. And best of all - unlike Disney's treasure hunts, this one was completely free!
Have fun!