Couple of Australians have been doing this since the 90's - I think they coined the term 'pooktre' to describe the form - https://www.pooktre.com/

Searching `Peter Cook Becky Northey tree furniture` gets you some nice pictures of their work, as they don't just 'do chair' -- though I suspect plenty of people have been doing this in various forms for centuries.

Well that’s flabbergasting.