elin...
Do it while the wood is still green and bendable, and do it in stages. Tie off the braiding every few inches with expandable tape. It will be a work in progress, and will take a few seasons to complete.
I'd use a single variety that ripens and goes dormant at the same time, and a variety that grows fast, and is long-lived..."Black Mission" etc. Go for the novelty, and plant/braid 3-4 different varieties. Either way....labor intensive when braiding time occurs...but fun to do. By the way, don't try this when stems get woody even though still young....they will snap. Trust me, I know.
I currently have 7 little "Black Mission" treelets braided together, that I started last year. As new, green, wood grows this season, I will continue to braid the stems to form a composite "trunk".
Why? Fun factor, and boredom.
Frank