Wikipedia
A tree-topper or treetopper is a decorative ornament placed on the top (or "crown") of a Christmas tree. Tree-toppers can take any form, but the most common shape is that of a star (a "Christmas star"); tree-toppers shaped as angels (a "Christmas angel") or finials (a "Christmas finial") are also very common. Other less common tree-toppers include paper rosettes, ribbon bows, Father Christmases or Santa Clauses, Christian crosses, Christmas owls, and sunbursts.
Tree-toppers may be made of blown glass, metal, or plastic, among other materials. Plastic tree-toppers are often electric and once connected with the tree's lights glow from within. Following World War II, various symbols of Christmastide, such as Santa Claus, were introduced as electrified tree-toppers.
Hans Christian Andersen's short story of " The Fir-Tree" describes the decoration of a Danish Christmas tree, including its topper, thus: