Help the Christmas tree photo from the start by selecting a great looking tree that fits nicely in your space. "Great" is as seen in your eyes. We have a tall ceiling over our tree's location and our tree height is limited to what I can haul home and make stay upright in the tree stand. Another limitation is that the top of the tree must be reachable using only a step ladder (scaffolding is not an option) and with our space not being large in width, it is nice to have enough space to be able to walk around the tree. The kids always want taller and the parents always want shorter. The parents can better tolerate taller if narrower enters the equation. With a narrow tree, height becomes easier to manage (except for the road clearance issue faced when hauling it home across the back of the SUV's Hitch Haul).
When decorating the tree, ensure that the strands of lights are all the same brand and model, or at least that all of the strands share the same bulb color and brightness. I learned that lesson a few years back when I needed to combine multiple exposures to balance out the brightness differences of our dual-brightness tree.
Do you have windows in the frame with your tree? If so, consider photographing during the blue hour which is really the blue minutes as there will likely be only a couple of minutes of ideal exterior brightness to balance with the indoor light levels, giving your images that extra wow factor. Shooting through that ideal time period will ensure the perfect minute is captured. You likely photographed a tree in the same location at the same time a year ago. Reviewing the EXIF information from a prior year's perfect photo will provide a close estimate of the perfect time for the blue minute shot this year. Then ensure you are set up and ready for that minute to arrive.
While reviewing images from prior years, look at the angles you captured to learn what works well and what doesn't. Repeat and avoid those compositions as makes sense. Also, check the camera settings used for the previous images for guidance on this year's camera settings. Note that changing out strands of lights can change the needed settings due to differing brightness.
Often, turning off all of the lights (or at least the brighter ones) in the house, aside from the Christmas lights, will result in the ideal lighting. If there are windows in the image, watch for reflections in those. Block any problematic reflections (such as the numbers on the microwave display) and take advantage of positive ones (such as the Christmas lights). For the image shared here, a couple of Post-It Notes were placed over the thermostat display. Note that double-pane windows may create double reflections.
With only the Christmas lights providing illumination, the environment is dark. While I like to use a wide aperture lens, I don't use a wide aperture for the Christmas tree photo. Stopping a wide aperture lens down to f/16 or so makes each light into a little starburst and stopped down wide aperture lenses tend to produce the best stars. The narrow aperture also makes it easy to keep the entire scene in focus.
Unless your lights are far brighter than ours, you can expect to need a long exposure at f/16. I usually use 30 seconds and sometimes bump the ISO up modestly to keep from having to wait for even longer exposures. Thus, a tripod is needed along with either a remote release or the self-timer used. I don't mind if the individual lights become slightly blown (pure white), but if an extra-bright decoration is in the frame, I will sometimes exposure bracket with an additional image captures.
Long exposures raise another problem for some of us. While most Christmas tree displays will be motionless, they may not always be perfectly so. Unless your Christmas tree is on a concrete floor, there is likely the potential for the floor to vibrate at least slightly when walked on. Hanging ornaments will likely be the first indicators that the floor has vibrated and if swinging, they will be blurred in 30-second exposures. Planning this shoot for when the rest of the family is not home (or is in bed) is a good idea. You might need to stand very still behind the camera for a couple of minutes before capturing the shot.
Think about the camera angle. A completely level camera is often desired for interior photography such as this and adjusting the camera height and distance from the tree provides the composition desired.
For this year's tree photo, I opted to use the Canon EOS R and RF 15-35mm F2.8 L IS USM Lens. The R's 30 MP resolution was very adequate for my needs and the RF 15-35 delivers impressive image quality. In addition, the 15mm focal length was very attractive for this image capture — and it became even more attractive during post processing. Despite being very careful to level the camera, I still managed to get a slightly tilted (0.6°) image. Straightening an image requires cropping (or creating missing details) and the 15mm angle of view gave me just enough additional angle of view to make that adjustment comfortable. Note how little barrel distortion is showing in this uncorrected image.
As soon as the perfect light was captured behind the windows, I pulled the couch and ottoman out of the way and pressed the shutter release of a second camera that was already set up, providing a completely different image.
From my family to yours, we wish you the merriest, joy-filled Christmas ever!