Your comments

Hi,
I'm also experiencing a lot of tabs jumping around. Also sometimes (much rare compared to jumping) a tab is not shown in the Sidewise but they exist in the Chrome. 
I second the above suggestions to restrict the level of tab hierarchy (to 1 for example, or removing completely) if it solves jumping issue...
Thanks for this nice tool, ilker.  
P.S. I started using Sidewise as a replacement to old good "side tabs" or "tree style tabs in FF" but I start to like it more. (it shows all the tabs from all open windows and the hibernation makes it more convenient.)