I installed Sidebery and just switched from TST to Sidebery, it kept whole tree structure and there's easily accessible option (from Sidebery's top menu) to switch back to TST.
The only problem so far I have with Sidebery is that it hasn't scrollbar on the left like TST but it seems that it's available in beta and should be included in new version.
So far I'm happy with it, I like how the text color on tabs is fading with time so you can see which tabs you visited recently.
On Firefox extension site it says "Last updated a year ago (Aug 28, 2022)". The beta has been dangling on github for half a year. I'm not installing a beta version which doesn't come from official site where at least some sort of review exists.
The only problem so far I have with Sidebery is that it hasn't scrollbar on the left like TST but it seems that it's available in beta and should be included in new version.
So far I'm happy with it, I like how the text color on tabs is fading with time so you can see which tabs you visited recently.