It just SOUNDS male to me. Really, really male. As male as
Christopher,
Matthew,
James.
You say it sounds feminine because it rhymes with
Kristen. I guess I don't get that connection because I've always seen
Kristen as one of the least feminine names out there. It reminds me of
Christian, which is also super male-sounding. And
Tristan and
Christian also rhyme, so there's even more of a male association for me.
*Shrugs* I do personally know two male Tristans. But throughout my life I've also heard of female Tristans, which has always made me think, "Really? But that's so... manly."