I think that the hierarchy approach could be improved by creating a cross-sectional layer through the hierarchy. (using big words that don’t mean anything)
Work->
-
-> Meetings
-
-> Programming
-
-> testing
-
-> training
-
-> training
Then each of then what you have is groupings inside and around there
ClientA
ClientB
I realize this could be very complicated to graph out if both were structured, or if it was just free tagging. Thus my request is one to be a hierarchy and the other to just feed as extra data within the category.