I set up 2 off-camera flashes in my den for Christmas morning. I will make a detailed post on this later. At any rate, I shot in manual with a shutter speed of 1/60 so that I would get the tree lights glowing without making the tree go too dark. From there, it's all about how much fill flash you use. If you have on-camera flash, I suggest bouncing it off the ceiling so the tree doesn't get blasted.
As for white balance, I balanced for flash and let the tree lights & lamps in the room glow yellow. I like the warm effect. If I wanted EVERYTHING white, I could have balanced for tungsten and gelled my flashes with CTO gels.
Examples:
This one was nice - the wrapping paper acted as a reflector giving my daughter a little extra glow.
The tree is a little blurred in the distance here:
My wife shot this with direct, on-camera flash -- I find the tree less interesting:
This is a portrait that I did last year with off-camera lighting and a 1/45 shutter f2.8. Thius was for our Christmas card.
Good luck!!!