I think this is an amazing game idea and for the most part a well executed one. however on the first few levels i felt like i was guessing where the tree i was placing was going to go. i'm suggesting something that indicated to the player where the tree will be being placed.
also I found myself stuck on this level . i placed the tree but nothing happpened after, I believe this would become very frustrating to a player who doesnt know what is going on. 
other than these smaller things the game is really nice and i love the soundtrack and sound effects. and that title screen.. mmmmmmm
keep up the work :)