The red channel on most of the older Nikon's (maybe new also) like D300, D700, etc. is very easy to blow out. This type of image is very demanding on a camera sensor. Check your camera's RGB histogram and I can almost guarantee you the red channel is clipped. There's no way you're going to get an even exposure on a Christmas tree without some amount of fill light (flash and drag the shutter). So try taking the same shot with about -.7 to 1 stop underexposure dialed in. But even with lot's of underexpose you'll never get a light bulb properly exposed without the rest of the tree going completely dark. I find 3/4 stop works well for most situations like red flowers, etc. Then you can bring some of the shadows back up in the software.