Walnuts are a simple thing you wouldn't automatically connect to the Christmas season. But walnuts are a wonderful symbol for Christmas.
The walnut tree was thought to be a holy tree in the same sort of way as the pine or fir tree. Walnuts were also thought to be a symbol of immortality and fertility. This means they're a symbol of birth. So there's a deep connection between this plant and the season of Christmas.
Walnuts are also a unique Christmas ornament. Depending on which type you choose they can work well with modern or more traditional looking decorations. Walnut shells can also be used to craft your own ornaments if you enjoy making craft items for your home.