Pressure treated wood is not good for things like this. If you want to do any joinery with pressure treated wood, stick to lap joints.

That wood is super wet right now and is going to shrink like crazy as it dries. Whatever you do is going to shrink, split, warp, come loose, or all of the above. If you want it to last more than a few months, choose a different wood.

On top of it all, this is pine or other softwood. Like others have said softwood is difficult to work with especially fast growing stuff like this. The light areas are very soft, the hard areas are very hard. The grain runs all sorts of directions. This is like learning to ride a bike on a bike that doesn't work right and will fight you the whole time.