Sometimes, scattering individual trees or rocks isn't enough; you want to scatter variations of objects within the same cluster. The ForestGroups actor solves this.
How it works: Think of ForestGroups as a procedural Geometry Collection. Instead of scattering one mesh per 1 cluster, you can group multiple different objects together, for example, you have 10 different Oak models, by default if you enable clustering, each cluster will scatter only 1 model per cluster which is naturally impossible. Then you going to have another group of lets say 15 spruces. You can now use these 2 groups inside of ForestTools (Both CPU and GPU) to have a variation inside of the cluster.