Block Material keeps switching back to ground

So I am rather new to using MCreator and I have been trying to make a custom tree for my biome, in which you need grass set as the block material for the trees to load, but after setting this it returns back to ground (which I believe is the default)

So if any fixes to this issue can be made it would be appreciated. (Because ive had enough of going back into the block, setting it to grass, and then seeing its back to ground!)