It's the trees BG from Yoshi's Island DS - Mario's Fleet Feet. These came with the mountains. I had to rip the trees, because of the palettes. It also overwrites palette 7. I ripped it, using LM Bitmap Pasting Feature.
Have fun using it! Sorry, I had to use palette 7 here.
This background is not acceptable to be approved for the following reasons:
Wrong map16 tiles:
I inserted everything but...
As you can see there's a lot of wrong tiles, presumably product of an incorrect remapping or leftovers from your personal rom which worked together.
Another minor issue (not a rejection reason, however) is that the Back Area Color is overwritten in both the sample level and pal/palmask files, but it isn't actually used anywhere.