This year marks the tenth anniversary for The Polyphonic Spree's annual holiday music show - an extravaganza they've held in Dallas each December - and the band is celebrating it with a live tour and new CD called Holidaydream, a collection of reworked versions of classics such as "Do You Hear What I Hear" and "White Christmas." On a recent morning, The Polyphonic Spree rolled up to NPR in their packed-to-the-gills bus and unloaded a small army of horn players, singers, and assorted gear for the largest Tiny Desk performance we've ever had. The band members spent much of the day getting ready for the three-song set and puzzling out the logistics of getting that many people behind Bob Boilen's desk. But, they said, it's a "human Tetris game" they've played many times before, and by the early afternoon they were ready to go. While many of the larger bands we host at the Tiny Desk often opt for stripped-down performances, what you see here with The Polyphonic Spree is pretty close to the band's full-on production, with a horn section, cello player, guitars and drums, and of course the full group of singers, led by the wonderfully effusive Tim DeLaughter. For this special holiday Tiny Desk performance, The Polyphonic Spree treated the NPR Music office to two traditional Christmas carols – "The Christmas Song (Chestnuts Roasting On An Open Fire)," "Silver Bells," and the relatively newer John Lennon classic "Happy Xmas (War Is Over)."