I think you will find that it is not Dean Martin infact it's Johnny Mathis, however it has been recorded by lots of people including an awful version by the Chipmonks, however by far the most popular and most used on adverts version is the original sung by PERRY COMO
Following on from above ( and by the way Dean Martin did do a version of this ) The song was written by a guy called Meredith Wilson in 1951 while staying at The Grand Hotel in Yarmouth Nova Scotia, it refered to the decorated Christmas tree in the hotel reception area This version is the original by Perry Como recorded in 1952.. click the link..