I tried recently to edit a lot of tree collisions, basically you need to have a part of the mesh (e.g. trunk) with collision enabled and other part(s) (e.g. foliage, small branches) with collision disabled...

From my in game tests it seems NiStringExtraData NCO works only in root node, so it is only good for 100% no collision objects (e.g. grass),

Is there a way to do collision/no collision parts using just NCO nodes without using a RootCollisionNode?