Is the holly a traditional decoration at Christmas time?

probably

Yes. The holly is a strong tree and thrives in harsh winters. When I was growing up, the saying was that the more berries the holly had, the harsher the winter would be. In pagan times this ability to survive and thrive and be strong was symbolized and they would probably decorate with it in the hope that they too would survive the winter the winter themselves. As the big pagan festival was celebrated during the winter solstice, it is likely that the Christians continued the tradition. The hymn "The Holly and the Ivy" clearly relates the symbolism - for example the holly's white berries denote Mary's pureness, the red berries denote Christ's blood and the leaves themselves are a reflection of Christ's crown of thorns. So, either way you prefer to view it, the holly is a traditional decoration.