People celebrate with Christmas trees because there was an appropriation of the Anglo and German tradition by the marketers in 30s New York.

Of course the Anglos and Germans appropriated it from the Pagans.

Of course the Pagans appropriated it from anyone else who thought trees were pretty enough to revere.

Religious iconography has not been different in the past, so why would it be now?

Another example: people say that we should keep the Christ in Christmas as opposed to using X-Mas. But in many Christian relgions in the world, there is a heavy use of a symbol called the Chi-Rho which is an appropriation of the Greek letters used to spell Christ's name, Khristos. This is the origin of X-Mas as it is often seen as deferential to NOT use the name of Christ and better to replace it with an initial: X. So we've appropriated a symbol from a language's alphabet that we don't use, to express a saying (Merry X-Mas) that we don't even understand anymore, to celebrate a holiday that many people don't understand past presents under a tree that we stole from another religion.

There is no such thing as cultural appropriation. It's just a mixing of cultures that the masses never cared about until recently.