I’m not exactly sure how this works, but it comes in useful. ssh within a
tmux session on one machine (a) to another machine that’s running tmux (b),
and tmux attach.
Now you have “double tmux”. I use control-f as my <PREFIX>, so
control-f s shows me a list of sessions on a. <PREFIX> control-b s
will do the same choose-tree -s on machine b.
When you’re ready to disconnect b, <PREFIX> control-b d does the
trick. (I’ve yet to try going three deep.)