I think baubles may be British. We would never say that in North America. Christmas balls would be understood, but I think most people would call them ornaments and then it covers everything on the tree.

P.S. I recommend against using the abbreviation "Xmas." You see it mostly in store advertisements. (I'm not sure what people use when texting). The names of holidays, particularly Christmas, are somewhat formal and it doesn't seem quite right to abbreviate them. I can't imagine anybody calling Independence Day "Indy Day" or "I-day."

In the United States, we would use neither one. The customary phrase is "Christmas ornaments." In part this is because shiny round globes are only one of many ornaments we hang on trees. This has been true for a long time! A story of an 1880s US Christmas describes a box of ornaments and says "There was every kind of gilt hanging-thing, from gilt pea-pods to butterflies on springs. There were shining flags and lanterns, and birdcages, and nests with birds sitting on them, baskets of fruit, gilt apples and bunches of grapes."

In American English, ‘bauble’ has a negative connotation. Showy, cheap-looking, worthless. ‘Christmas ball’ doesn’t mean anything. You could possibly say ‘Christmas tree ball’. The tree was decorated simply with silver and gold balls. I find Christmas trees decorated with ball-shaped ornaments sad. I like trees where every ornament has a meaning. That’s what was on my Christmas tree growing up - the angel passed down from my great-grandmother, the decorations made by the kids in kindergarten, the ornaments bought on vacation etc. A good Christmas tree tells a story.

I agree with Michelle. In Australia, we use 'baubles' more and I have heard it regularly in the UK as well. 'Decorations' would more a more common word that covers everything on the tree in Australia and possibly the UK as well. We may say 'ornaments' in Australia (to refer to everything), but it sounds more formal or North American to me.