Most of the English-speaking world would say that they hang ornaments (noun - lovely, decorative adornments) on their Christmas trees. But not all of them. The following label ripped from a recent dollar store purchase proves the point --
The Chinese manufacturers of this lovely, decorative adornment could not have known that they were actually referencing the down-home version of the word ornament that is used here in the southern United States, as in:
"VERN! Git up 'ere and hang them ORNEYMENTS up high on the tree!"
But then, things could always be worse --