The reality is that Christmas trees on government property have nothing to do with accommodating Christians and everything to do with slapping Christian branding on institutions that represent Christians and non-Christians alike.
How is it "Christian branding" when I have a tree??
How is it "Christian branding" when Japanese atheists have trees??
It's just a seasonal and cultural decoration that transcends religion at this point in time. It was once associated with pagan beliefs, and then it was no longer.
It was once associated with Christian beliefs, but there are plenty of us who now decorate trees as a representation of culture who are ourselves outside of the Christian religion.
Christmas trees are awesome and don't have to be religious. You dang humbuggers are all just trying to kill the Christmas spirit and seasonal aesthetic pretending that this is somehow about religious endorsement when plenty of us non-Christians of many varieties decorate trees for the season.
Nativities are clearly religious and if you want to keep them off of public land be my guest, but leave the dang trees alone!! Unless you're using specifically Christian or pagan ornaments, there isn't anything inherently religious about a tree covered in lights and baubles.