The video is a basic introduction to the fast-growing hierarchy. They do state where Graham's Number sits in the hierarchy, but the explanation doesn't go as far as to say where TREE sits.
Faster than anything in the Wainer hierarchy (which ends at $f_{\epsilon_{0}}(n)$. But it's reasonably easy to define a fast-growing hierarchy that uses the Veblen hierarchy of ordinals for the subscripts. Then TREE is $f_{svo}(n)$ where $svo$ is the limit of the finitary veblen sequence as the number of elements goes to $\omega$ (aka the small veblen ordinal).