Apologies if "is the movie accurate" post are too common. I'm watching the movie now and I'm only wiki-level familiar with the history. Greenery has pagan roots adopted by Christians, but would a single large decorated tree be accurate for the period?
Just checked 1968 film version.
I wrote a (actually not so) relevant comment for this following post, Origin of Christmas tree and Christmas lights, so I adds some points also here (though I'm not a specialist of this kind of tradition):
In short, there was at least no Christmas Tree in 1183, as decorated in the film.