Tree of whispers has 10 box’s in the progress bar right? well each activity should be worth 2 box’s with 5 total. so lets say red, blue, green, yellow, orange. that could correspond to - seasonal, boss (dura or andy lets say), stronghold/Legion if stronghold are all done, hordes, pit. After all 5 are complete you get a Cache.
What they really want you to do is buy the battlepass and a few cosmetics and they want to put in the least amount of effort and cost to accomplish it. If they do anything else it is in hopes of you making those purchases.