This answer from /u/Georgy_K_Zhukov is a fantastic write up on the Truce. This answer from /u/Minardi-Man is short, but hits on some key points you might find valuable. Finally, this answer from /u/DuxBelisarius has an interesting comment chain about how our dominant cultural perceptions of the truce came to be.

In short, it was a sporadic, "bottom-up" event that occurred in localized sections of the front and was by no means universal. High Command did not order it, but rather, in the places it did occur, it happened informally through the initiative of the men. It also only really happened in sectors with the British and Germans, and even then not uniformly or universally on the front.