superficially, there are similarities, but they really are separate concepts IIUC

my advice to research this would be to find Peter Todd's original thread here on Bitcointalk (there might even be in that thread a younger version of me, probably not adding much to the conversation ), also try to look through the bitcoin-dev mailing list archives to find a corresponding thread.



not in any detail. I know so little about tree-chains and DAGs that it's better I don't comment right now. But you can make a basic observation: no-one's developed any separate cryptocoin using either concept that has seen any notable success. The most prominent was IOTA, and it suffered the typical crpyotcurrency life-cycle; ICO flavor of the month -> slow decline in interest/relevance.

Possibly there's some interesting research in these areas too, but I'm not aware of anything that's caught fire at all.