Select a color scheme for the tree. Purchase new or antique buttons in the color scheme in a variety of sizes (small, medium, and large). Sort the buttons by size and color.
Beginning with the largest buttons, insert a pin into a button hole and pin the button to the cone. Place the largest buttons randomly around the lower portion of the tree. (If desired, dip the pin shaft into glue before inserting into the cone.) Layer some contrasting smaller buttons onto the large buttons. As you are working, check your tree for balance of button color and size; adjust as necessary. Continue by placing medium buttons of contrasting colors adjacent to the large buttons.
Fill in the gaps between the larger buttons with the smaller buttons. Add buttons until the foam cone is completely covered.
Use small buttons at the top of the tree. Add a star or other ornament to the top of the tree.