I definitely wouldn't use flash, as it creates distracting and harsh shadows, and produces the wrong kind of light. Use a tripod and set the white balance to tungsten.
Also try manual white balance to see which produces the nicest look. It would also help to have some ambient light nearby, as long as it's tungsten as well. The christmas lights don't put out enough to light up the entire tree. If you can get an exposure of several seconds (lowest ISO and f/22), you could use a flashlight to shine over the entire tree.
Shooting in RAW allows you to fine tune the white balance, which is one of the main culprits here. You may not want to hear this, but I'd recommend getting and learning Lightroom. It helps so much in processing an image, especially with tricky situations like yours. Even Photoshop Elements should allow you to process RAW files. (Check before you buy, because I don't know for sure.)
The following shot is one I took five years ago of a friends tree.
This next one is the same shot I processed today.
And this is a variation on doing on doing the whole tree. Sometimes a close-up tells the story better. Though it's all about personal preference.
Obviously, I used a star filter, which will likely please some and annoy others.
The thing is, don't stop experimenting. And asking questions. You might want to join the NAPP (
Learn Adobe Photoshop, Lightroom and Digital Photography | NAPP) as they have lots of helpful tips in their magazine and on their web site. That is, if you're ready to invest in the full-blown version of Photoshop.
Good luck and let us know when you figure out what works for you.