Basque cannot belong on that tree. It’s non-IE.
I don’t think that anyone knows exactly WHAT it is (non-IE or otherwise), unless there have been some new research findings that I haven’t heard about, yet :) Since it doesn’t really “belong” anywhere (again, last I heard), and it’s a language of Europe, it came to mind. Just wanted to throw it out there for those interested :)
Another missing language is Afrikaans, which has now evolved far enough from Dutch that it is considered a separate language, rather than just a dialect of Dutch.