The Christmas song is We Wish You a Merry Christmas.

We Wish You a Merry Christmas is a Christmas carol originating from the West of England, born in the 16th century. The earliest current lyrics were collected by the English politician and writer Davis Gilbert around 1822, and the song had also been published by William Sandy in 1833.

From the lyrics of the song, we can learn that the song originated from the 19th-century customs of the upper class in the west of England, and the "figgy pudding" in the lyrics was one of the most common foods that the upper class at that time would enjoy at their Christmas feasts. Of course, in the West of England dialect "figgy pudding" is more of a raisin pudding, so it doesn't have to contain figs.