How to make a custom trunk placer?

I have been attempting to make a custom trunk placer to use in a .json file to make some wacky trees. I have tried the inbuilt code editor AND IntelliJ to make the .java files, but I can't get it to work because MCreator has no worldgen/tree directory. Can I add extra directories to my MCreator project's src? From there, what resource should I look to to learn how to make tree placers in neoforge? Do I need to put something in Mod.java main class too?