Christmas decor (4)
'christmas decor' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tree that I've seen before include "Genealogist's graphic" , "Box, perhaps" , "Branching diagram" , "Laurel, perhaps" , "Ash or elm, for example" .)
(Other definitions for holly that I've seen before include "Shrub with scarlet berries" , "Prickly-leaved shrub" , "Shrub with red berries" , "Prickly Christmas decoration" , "Evergreen used in wreaths" .)