Thanks Jim for the link to "Is WikiTree non-profit?" That's what I needed, but I couldn't find it. The next section, "Is our collaborative tree public domain?" was also helpful.
I was pretty sure WikiTree content wasn't under the same kind of licensing that Commons is. But now we can say it definitely isn't.
He was so nice to just send me the files & let me do whatever I want with then, I hate to bother him to attach a license to the content on WikiTree. I guess I'll just have to go through the trouble of forwarding his written permission to the moderators at Commons. It just would've been easier for me if I'd been able to check the box saying it was already licensed under Creative Commons. But it's fine. It'll all work out.