“Christmas Tree Farm” celebrates childhood memories — Taylor Swift grew up on a farm — from an adult’s distance. In the intro, she croons about grown-up stress over 1950s-style strings. But then a modernized wall of sound whisks her into happier thoughts — and also into Mariah Carey’s (and Phil Spector’s) seasonal territory. Behind the sleigh bells and chimes, it turns out Swift is only wishing she could be back on the farm, but a euphoric final refrain — “Baby, baby, Merry Christmas!” — sweeps any misgivings away. PARELES