The Christmas decorations in Thailand usually go up towards the end of November. You will mainly see them at the large shopping malls. A number of hotels and shopping malls in Bangkok will compete to have the largest or the brightest lit Christmas tree. You can also buy your own plastic tree and decorations at the hypermarkets such as Tesco Lotus and Big C. At my house, the tree will stay up for the 12 days after Christmas Day. However, many Thais keep them up for much longer. For them, Christmas and New Year is one long event that has been merged into one celebration.