Chrome doesn't support the APIs needed to make a full Tree-style Tabs replacement. Anything that attempts to do it by necessity runs in a separate window disconnected from your browser.

So it's there, but it's nowhere near as seamless and convenient as it is in Firefox.

As @slavak mentions, Chrome APIs are far more hobbled and every tree-style implementation I've seen has been glaringly deficient in comparison to Tree-style-tabs on Firefox. TST should be the way all browsers handle tabs, especially considering that vertical screen real-estate is far more expensive. I've been using it for 6+ years and can't imagine browsing any other way.