Both can be correct. However, if you want to go with the second option, I would define your top level service as “Communication, Collaboration & Analytics” then the a child service for each “Communication”, “Collaboration”, then have your offerings related to each of the child services. I always tend to think that everything rolls up to one service a some point. Honestly, it can be broken down even further. Take for example O365, which has offerings of itself like E1, E2, etc. That would be 3 tiers of services and offerings. Unless, all you are offering is one O365 package. Hope this makes sense, if not, let me know and I can help you understand how I helped organization build their CMDB using CSDM methodology.