Can Muslims have a Christmas tree?

Generally speaking, no, Muslims do not celebrate Christmas. According to the scriptures, the celebration of Non Islamic religious festivals is not permitted. However it's not to say no Muslims celebrate Christmas or or make a small gesture like having Christmas dinner, exchanging gifts or getting the day off work etc. This may be for a myriad of reasons. Their families may not be Muslims so they still celebrate it as a family affair and some people may see Christmas as more of a national tradition rather than religious, for others it may have something to do with school or work etc, invitation by friends or neighbours and some may wish to learn about or sample other cultures. Not all Muslims are devoutly religious, there are many liberal ones who don't practice Islam by the book so would have a different outlook.