No, Tristania is not a goth band, because they play Symphonic/Gothic Metal, while goth music consists of Gothic Rock and its derived genres, like Deathrock, Darkwave, Ethereal Wave, and Coldwave.

However, they do have a significant goth influence and even have some goth songs in their repertoire, like "Angellore", "Cease To Exist", and "Cure".

If you want to dive into the goth music scene, some of the bands that might appeal to you if you enjoy Tristania are Elusive, Fields Of The Nephilim, and Mors Syphilitica.