It's possible to play Christmas carols with humor but not mockery. So, yes, there's a bit of an eggnog buzz in the wah-wah muted horns of "It Came Upon a Midnight Clear," and a soca lilt to "Jingle Bells." But in this case, "humor" means serious-minded but without solemnity or sentimentality.
In fact, Bley plays it as straight-up as her title suggests: she (mostly on piano) and bassist/partner Steve Swallow are joined by a brass quintet put together by Berlin bass-trombone and tuba player Ed Partyka — a sound as trad-Xmas as it gets. But listen to album opener "O Tannenbaum" as that brass quintet moves incrementally, a half-step at a time, into extended harmonies, a trumpet cadenza, and a final jazz chord.
There are the Christmas touches of glockenspiel, celesta, and chimes here and there, but mostly Bley is looking for new ways to dig into this too-familiar material. Sometimes that means turning a melody like "Away in a Manger" over to Swallow for a poignant high-note reading — his five-string bass singing at the top of its register — before a horn enters with "Middle Eastern" scales, the tension between minor and major coloring the song's warm reassurances. And sometimes that means just letting a trumpet blow jazz swing over walking bass, as on the Bley original "Hell's Bells." The writing and playing here are so beautiful, in fact, that "Christmas music" hardly does it justice.