Trees spawning improperly in the nether

After a while, I finally got the biome I made to spawn in the nether. I created 64 different structure block designs for alternative trees. I then tried to import one to make sure it worked. I had the requirements as normal positioning offset, they spawned in the nether, in the biome, and on the "Ground (grass) block." Nothing spawned whatsoever. I removed the Ground (grass) block spawning dependency and they began spawning in midair or in the solid walls of the nether. Does anyone know how to fix this?  

If they spawn, they spawn like this: https://ibb.co/GMvDxrB

They also spawn like this: https://ibb.co/H4xjGB2

I want them to spawn like this: https://ibb.co/mthQxnN