From Longman Dictionary of Contemporary EnglishChristmas treeˈChristmas tree noun [countable] 
DHa fir tree that people put in their houses and decorate for Christmas
DHa fir tree that people put in their houses and decorate for ChristmasExamples from the Corpus
Christmas tree• Two days before the President's visit they began to dress the mast like a Christmas tree.• The chart resembled a Christmas tree, with John Gutfreund on the top and us at the bottom.• Now she was under a Christmas tree, the most beautiful and best-decorated tree she could imagine.• There was a Christmas tree in the living room and a surfing video on the television.• O Christmas tree, O Christmas tree / How brightly shine thy candles.• I du n no how tall it is, but the Christmas tree outside the caff is blummin huge.• I go and sit on the bench in front of the Christmas tree and stare at it.• Prevent pine-needle fall-out from covering your floors when removing your Christmas tree. 