So a Charlie brown Xmas Tree is what? A abre tree? (the reference is lost on a Brit like me!!!)
Oh, it's a bit of an explanation.
At Christmas time here, there is a half-hour cartoon that runs, called "A Charlie Brown Christmas".
Charlie Brown is not feelng Christmas, and he is made the director of the school play, in an effort to make him get into the holiday spirit.
The other kids send him to a place to get a pink aluminum tree. He returns with a live tree, that is very similiar to the pic I posted above. They all laugh at him, and his tree.
After another character explains what the real meaning of Christmas is, Charlie Brown puts a Chirstmas ball on the tree, and it bends over, he thinks he's killed it, and leaves.
The other kids decide the tree just needs 'love', and they wrap a blanket around the base, and add all the decorations they have, transforming it into a full, and beautiful tree.
When someone says they have a "charlie brown tree", it means one that is pretty sparse and beat up looking.