Also known as: treetopper
From 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, though the most common include a star (representing the Star of Bethlehem), finial, angel ("Christmas angel"), or fairy. Additional forms range from a paper rosette, ribbon bow, Father Christmas or Santa Claus, to a Christian cross, owl, white dove, spike, or sunburst.
Tree-toppers may be made of from a wide range of materials. Modern plastic tree-toppers are often electric and once connected with the tree's lights offer a gentle glow. Following World War II, various symbols of Christmastide, such as Santa Claus, were introduced as electrified tree-toppers.