Prepare a paper pattern of a half-circle. My pattern is half of a 19" circle.
Place two contrasting fabrics right sides together and pin the pattern on top. (If your fabric is directional, remember that the top of the napkin is the straight edge.)
Stitch around the pattern leaving an opening on the straight side.
Remove the pattern. Cut out the piece 1/4" beyond the stitching. Trim the corners.
Turn the semi-circle right side out through the opening. Carefully press the edge, turning under the raw edges at the opening. Top-stitch all the way around. This will finish the opening.
Place the napkin right side up and mark the centre of the straight edge. Measure two inches to the right of the centre and mark this point. This point will be the top of your tree. All the folds start at this point.
Pick up the right side of the napkin and fold back at the point you just marked. Line up the straight edges at the top.
Move the straight edge down to the right so that it lies along the vertical fold at the right hand side.
Lift the napkin and fold the straight edge at the top back and down so that it lies underneath the other layers along the vertical fold. Press these folds with a hot iron.
Your Christmas tree is ready to decorate your table.
Things to try:
Decorate the curved edge of the napkin with lace, rickrack, or fancy stitching.
Experiment with starting the fold closer to the centre or farther away from the centre.
Add a "tree trunk" at the bottom of the tree. This can be inserted into the curved seam before you sew it.