The melody of Once Upon A Christmas by Dolly Parton runs 233 notes across 24 bars, 3:10 long in Am at 66 beats per minute. The tab sits low on the neck, mostly under the fourth fret, one note at a time — no chords to barre and no strumming pattern to keep up with. A piano backing track plays the chords and bass underneath, so the line you are learning sounds like the record even at half speed.
Prefer to strum and sing it instead? Once Upon A Christmas chords and lyrics.