Scene Struct: Implement drag and drop Entity parenting/unparenting. Implement Type based sorting (make default) that sorts by id but first replicated, then temporary/local. Make TundraUndoCommand base class for operations that are expensive for the tree, these will have common interface for start/stop execution so sorting can be properly disabled/enabled. Optimize EntityItem sorting. Implement parent Entity to/from manipulation when a Group is involved. NOTE: Mixing groups and entity parenting still has some bugs, i would not recommend mixing the two. You can always reopen Scene Struct to fix any visibility issues. Additionally when they are mixed the Group items child num will lie to you, this cannot be fixed with the current data structures. When it comes down to mixin, Entity parenting always takes presedence in the tree hierarchy.