The Christmas Tree is one of the most iconic pieces of the holidays and it is actually a Scandinavian and Norse Winter Solstice Tradition. In old times, People of the Norse lands would bring evergreen trees into their homes as a way of ensuring the life that stirs even in the cold grasp of winter. The evergreen itself represents life, rebirth and stamina; all things people would need to have in order to survive the harsh climate of winter and see another spring. Fir trees in particular represented the tree of life. They most likely felt that by honoring the trees that posess such qualities, the tree may bestow those qualities upon the household who honored it thus ensuring a safe winter.
The act of kissing under the mistletoe has become a kind of social convention in today's light but originally, it was considered a fertility ritual. You see Mistletoe is regarded as a sacred plant to the Greeks and the Scandinavians and kissing under it ensures fertility and romance to the guy or gal who is kissed underneath it. In the 1700s in England, the "Kissing Ball" which was a decorated ball of mistletoe, was hung and if a young lady found herself underneath it, she would need to be kissed or else she would not be expected to marry in the following year.
Even Saint Nick has his pagan roots! He was based on a 4th Century Lycian St. Nicholas, who gave presents to the poor, children and in one instance he bestowed dowries to the three daughters of a poor man saving them from a life of prostitution. The common perception of him however is mostly Norse in nature. The original Saint Nicholas did not ride a magical reindeer, travel all over the world giving kids gifts or really have anything to do with the holidays at all. It is a widely accepted fact that the popular imagery of saint nick is really that of The Norse god Odin and his 8 legged horse Sleipner who was able to leap great distances (hence the flying reindeer). Odin was portrayed as an old man with a white beard much like Santa Clause. In the winter, children would leave carrots and straw for Sleipner in shoes underneath their chimneys and when Odin and Sleipner flew by, he would replace the straw and carrots with presents (hence leaving cookies for Santa and stockings by the chimney) It wasn't until Dutch Settlers arrived in Amsterdam that St. Nick morphed into the modern Santa Clause.
The Roman celebration of the winter season was known as Saturnalia, celebrating Saturn. The whole season was called "Dies Natalis Invicti Solis" or the birthday of the unconquered sun. Anyways, Saturnalia was marked by great merrymaking and partying and from this, the Mummers were born who were groups of costumed singers and dancers who went from house to house to entertain their neighbors. This, in later years turned into Christmas Caroling.
In ancient Babylon, the Feast of the Son of Isis is celebrated during what is not Christmas Day. The feast consisted of Partying, eating, drinking and of course gift giving. These practices seemed to resonate into the Modern Christmas Celebrations we have today.