Marti showed this piecing technique on "Simply Quilts" Episode 550
1. Using a strip of tape, mark a new cutting line on "piece a", just above the asterisk on the template. This is approximate and should be adequate for any size tree trunk. Mark the three dots. (The dot for the tip of the a piece is not needed.)
2. Sew the a pieces into pairs as shown in the instructions, but use dot-to-edge sewing, not dot-to-dot.
3. Substitute the diagram below for diagram 3a:
Trim any uneven edges along the circular opening. Sew all the units together, leaving the last seam unsewn.
4. Follow the Giant Dahlia instructions. Sew the arcs together, leaving the last seam unsewn.
5. Layer and quilt. Bind with bias tape. OR line the tree skirt, leaving an opening on one edge. Turn through the opening and sew the opening closed.