Definition of christmas trees:
(n) :
An evergreen tree (usually a conifer), or an artificial tree made to resemble this, which is typically decorated with lights and ornaments and often an angel or star at its tip, and used as a decoration during the Christmas holiday season.
(n) :
(by extension) Something which resembles a Christmas tree (sense 1) in appearance (for example, in having coloured lights) or shape.
(n) :
(informal) Something which is elaborately decorated.
(n) :
(by extension) A Christmas party, especially one organized for (underprivileged) children by a charity, a school, etc.
(n) :
(Australia) Often with a descriptive word: any of several shrubs or trees native to Australia which bloom in summer at the end of the year around Christmastime, and so may be used as a Christmas decoration; especially the fire tree or moodjar (Nuytsia floribunda).
(n) :
(New Zealand) Synonym of pohutukawa (“a coastal evergreen tree, Metrosideros excelsa, native to New Zealand and producing a brilliant display of red flowers with prominent stamens around Christmastime”)