I can see both sides. I believe that the Christmasteers have good intentions with their tradition but I wouldn't question the faith and discipline of those that choose not to take such liberties.
Personally, I wouldn’t consider it idolatry even if you did have religous symbols and angels on it - mine does. You’re still not worshipping the tree. I think of a tree like a blank canvas - something to decorate however you like that brings happiness and joy during a time of celebration regarding the birth of Christ. It’s Christ we worship, not the tree. If that makes me pagan, or some kind of heathen in the eyes of MEN, then fine, I think God knows my heart. This idea of idolatry is taken too far in my mind - in ancient times there used to be whole religions built around a made-up, and entirely temporal diety - think golden calf -that’s idolatry, not the use of a physical object to glorify God. I’m sure we can find some Christians who find EVERYTHING sinful or idolatrous including the use of the cross or any representations of Christ or earthly things...but personally I don’t think God intended us to be miserable or gave us great artistic, literary, engineering, and other skills to celebrate all aspects of life but the Creator of it.