I don't know of anyone who has been able to keep them for over a year or so. I actually got a christmas tree rock with my live rock but it didn't last more than 6 months. I think they probably need better conditions than our tanks provide. But if I had to guess:
1. Good conditions to keep the coral alive. This includes strong light, good flow, low organics, and adequate Ca/Alk for building.
2. Something food wise for the christmas tree worms. Whether thats phytoplankton or zoaplankton, I don't know. I didn't provide this for my tank which may be why mine didn't make it.
Anyway they are very pretty but dificult to keep, especially long term. Hopefully someone else will offer better suggestions for care.