I gave it another shot just now. It doesn't seem to want to import correctly and if I work around the issue the trees won't look right. It could be that I'm still importing them incorrectly but I've tried importing into level, dragging the full folder into the game content, and even individually importing the assets and plugging them together manually.
Manually plugging the assets in does work but the trees don't look right and I think that could be because I'm not too sure how to properly mask things out and all that.
I feel bad bugging you but do you have any other ideas I could try?