Some people like to overlap the trees like that, while others (like myself) don't. It's really a matter of personal preference, though sometimes the overlap can cause some confusion on the perspective.
That being said, since these are 2D and not 3D, I would recommend that you not overlap them, Alucus. As I said, it causes some perspective confusion. The sprites themselves are really well done. I'm just going to run through Pallet Town at the moment. The trees look like they came straight from the game. You did a really good job with the palette, the shape, and the proportions. The colors are just right, and the shape is spot on. I would only suggest that you clean it up just a little bit. There is just the slightest bit of jagginess in it. The house is excellent. The colors are great, and accurately represent they way they would look in game. The shape and perspective are excellent, too. Nothing really to say on the houses. The lab is pretty good, too, but could use a little touching up. The palette seems a bit dark. Maybe lighten it up a few shades and see how it goes. The shape is great, nothing to say there. The windows at the top look a little odd. I haven't gotten to Pallet Town in the game yet, so I don't know what the lab looks like, but I think it would look better with more round windows. I'm not going to comment on the ground, path, flower, and fence tiles, as there is nothing wrong with them.
Overall, great job.
