The construction of the tree skirt is very simple. You can use any circle skirt pattern and viola you have a skirt for your tree. The trick comes in when finishing the seams so they won't fray. From what I read, one method is to make two entire tree skirts and sew them with right sides together, turn them, then finish the opening. I really didn't want to come up with that much fabric, so I did French seams.
Using my Circle Skirt Pattern to Make a Star Tree Skirt
How I did French Seams
To finish the top and bottom of the skirt, I made facings. I used muslin because it is super light weight and inexpensive. I included a picture below of the top facing. It looks like bias tape with it is finished, but is much easier to work with all the angles of the skirt. I added the bottom facing to each of the main panels before sewing them together (ie sew two blue together, then add facing, then sew to a finished red panel).
How I did the Bottom Facings
Once the bottom facings were done, I sewed all the panels together, then finished the rest of the French seams, but not the final two edges of the skirt. Finishing the top of the skirt with a facing was much easier than anticipated, too.
How I did the Top Facing
Then all that was left was to finish the two last edges of the skirt by folding them over twice, pressing and stitching. I didn't add ties because my tree skirt needed to go over a crate (put there to keep a naughty rabbit from eating the tree) and I wanted to make sure it would fit before committing to sewing on ties. It fits perfectly (husband thought it was going to be humongous lol), but now the problem is snagging it when the rabbit isn't sleeping on it so I can add those ties!