The growth of a pine tree is examined by preparing "tree cookies" (cross-sectional disks) between whorls of branches. The use of Christmas trees allows the tree cookies to be obtained with inexpensive, commonly available tools. Students use the tree cookies to investigate the annual growth of the tree and how it corresponds to the number of whorls on the tree. Height-diameter and height-age relationships are also investigated. While aimed at high school classes, the procedure can be adapted for younger students.