Better styling of tabs: It does not really look as tabs. Missing of clear separation between items  or visual grouping makes it more difficult to quickly scan through items. Take a look at Firefox extension "Tree styled tabs". It is not perfect but they are styled as tabs, and has many more great and useful functions.

Auto-collapse unfocused tree: You can also see it at above mentioned plugins. If you have multiple trees opened, they all collapse except the tree with currently selected tab. Not that useful in daily browsing but great for researching with 50+ tabs opened. 

I also have problem that I have to reinstall your extensions every time I open chrome (latest version). Clicking on the icon does nothing.