The tileset doesn't need to be updated. This is one file called treetop.png, which sits above the "stumps" of trees to allow the effect of letting a person walk behind the tree top.

All you have to do is, with the current tileset on, find a tree on the tileset that doesn't use treetop.png. Take a screenshot. Crop the photo and remove the background. This should make it the same size as the green treetop.png, but some adjustments might be necessary to make sure they overlap exactly. This is not complicated stuff, anyone with minimal Photoshop knowledge could do this easily, and it wouldn't take more than 5 minutes.

Then upload via RC. Oh wait, you need a staff member that actually gives a damn for that part.