Here is a list of stuff I have found so far just by porting my mod.

OrePlacedFeatures.modifiers
OrePlacedFeatures.modifiersWithCount
OrePlacedFeatures.modifiersWithRarity

TreeConfiguredFeatures.builder
TreeConfiguredFeatures.oak/birch/superBirch/jungle/fancyOak

TreeDecoratorType's constructor

Please leave a comment if you have any more suggestions.