People decorate their homes and trees during Christmas because it symbolizes the joy and spirit of the holiday season. Decorating helps create a festive atmosphere, adds a sense of warmth and beauty to the environment, and allows individuals to express their creativity and individuality. Additionally, the act of decorating has become a tradition for many families and communities, providing a sense of unity and shared experience. The bright lights and colorful decorations serve as a reminder of the season's message of hope, love, and goodwill towards all.