1. Wash the wool in very hot water and dry it in the dryer; repeat. This "felts" the wool so that it won't ravel, eliminating the need to line or hem the skirt.
2. Fold the fabric so the selvages meet, then fold again so the raw edges meet. You should have a square. Along each folded side, measure and mark 24 inches from the point where the folds meet. Using a 24-inch-long piece of string, a pushpin, and a water-erasable marker, draw a curved line from point to point. Cut along this line, then open out the fabric. You should have a 48-inch-diameter circle.
3. Refold the circle in half and press. Fold in half two more times and press to create eight pressed lines.
4. Open out the folded circle. At the center, draw a 3-1/4-inch diameter circle, using a disappearing marker. This will be the opening for the tree trunk. Cut along one pressed line and around the circle.
5. With the disappearing marker and a ruler, draw placement lines for the ribbon, using the pressed lines as a guide. At the center opening, allow 1/4 inch between the ribbons; at the bottom edge, allow 3/4 inch between the ribbons. Center the pressed line between the ribbons.
6. Pin the ribbons in place, leaving about 1/2 inch extending beyond the top and bottom edges of the tree skirt. Carefully machine-baste the ribbons in place. Fold the ribbon at the bottom edge to the back of the tree skirt. Thread the sewing machine with invisible thread in the needle and with thread matching the ribbon in the bobbin. Topstitch along both sides of the ribbon. Use a #3 stitch setting if your machine allows.
7. Trim the ribbons at the top; zigzag-stitch around the opening to finish the edge. Steam the skirt on both sides. Hand-stitch one button to the left or right of the ribbon stripes.