Trees are decorated at Christmas because it's a beautiful and joyful tradition that adds to the overall holiday spirit. It's a way to bring the outside world inside and create a festive atmosphere in our homes and communities. The tradition of decorating trees dates back to ancient times when people used to bring greenery indoors during the winter months to symbolize life and renewal. Today, decorating trees is a way to celebrate the holiday season and create a sense of warmth and joy. It's also a way to bring families together and create lasting memories.