A masculine bearer of the name is Trix Solier, the title hero of two novels by Sergey_Lukyanenko (AFAIK not yet published in English, but a German translation is available).
I hope no one has named their daughter this instead of Beatrix or even Bellatrix, which is a cool name, by the way. The name sounds very incopmplete, nickname-y, minimalist, and too youthful for a person past the age of 20. Besides, a girl named Trix would certainbly get a few jokes related to 'tricks'.