In the world, you can find 1-5 blocks of foliage that are not far from the main tree, but this foliage is not attached to the tree in any way. Also, some trees lack foliage until you cut it down.

One and the same tree, before and after cutting down.

That is odd. Does a log out/close Minecraft and restart change how it looks before cutting down?
The world seed would help in troubleshooting. Why are you out at x=10M+?