You can't delete your whole tree at once on WikiTree. This is because it's a collaborative site, so other people may have connected to your tree. In that case you'd be deleting other people's work, too.
I took a look at your tree, though, and it appears that most of your profiles are private, anyway. If you click on the "Profile public view" link on a profile, you'll see what other people would see if they went to your tree. When your profiles are private, it's not much. See here for more info about the privacy levels: http://www.wikitree.com/wiki/Privacy
I hope that helps!