Thanks a lot :))))
Yeah, it's built round it. Underneath the branch itself I made a section of the roof just with lead sheet. The tree doesn't move at that section, it's a very bi diameter crotch.
ATM i'm using the underneath for timber storage. I'm in two minds about what to do about it TBH. In future there will be decking which will close off the front. There's membrane under there, nothing living so far, I think it's too exposed just now. Someone said to me at some point, that if i close it off, it makes it more attractive to rodents, and they will find their way in. Unsure, will decide on that another day!