I hope someone has a more complete answer for you, but Gedmatch is undergoing a transition. They previously had two websites, Gedmatch (the traditional one) and Gedmatch Genesis, which accepted kits from DNA companies that had a different type of chip that wasn't easily compared to the kits on the original site.
Recently, they have progressed to a point where they merged the two sites, so that all kits can be compared. They are no longer accepting uploads to the "old" site. The old site had a lot of good features, including the Wikitree link. The newly merged site doesn't seem to have the ability to show the Wikitree links-- "yet". I assume (but don't really know) that some day they will add some functions that were on the original site that are not available at the new site.
I'm hoping that patience is the key. I don't think you can add your Wikitree information right now.