I don’t have a Christmas tree, but the birds in my garden do! You can purchase suet balls and feeders, but I thought homemade might be nicer. I made some suet balls by blending shortening, seed, some crushed peanuts and a little honey (a bit messy to make but not too bad). Then I used leftover fruit bags (in different colors), tied them up and hung them on the little pine in my garden.
Please note: these are also attractive to squirrels. The day after I hung mine I looked out to see a squirrel sitting up tall next to the tree. He had removed the entire green ball from the low branch and was holding it in his little greedy hands. Oh well!