You'll need the following before you get started:
-- stiff interfacing; I prefer Pellon double-sided fusible interfacing for this project
-- sharp scissors
-- fabric; I think this is a great place to use up scraps, especially surface-designed cloth
-- fusible web
-- embellishments such as beads, embroidery thread, and photo transfers
-- Glue or matte medium
-- coordinating paint for the edges and a tool for applying paint; I like to use a foam brush
Decide on the shape of your tree. (Since triangles are easy to use and can be made in any size to suit your table, I'll use that shape for illustration purposes here. The same directions apply to any tree shape you use. ) Cut the shape out of the stiff interfacing four times, taking care to keep the size consistent with each piece you cut.
Mark the center line of each form. You'll cut on each side of the line to make an opening that's just a bit wider than double the width of the interfacing. Be sure to cut from the bottom up on half the triangles, and from the top down on the others. You'll need two forms with "bottom up" cuts and two with "top down" cuts, for a total of four forms.
This pair of forms will slide together to make a tree. Ideally, you want the cuts to almost "meet" in the middle. Try it out. Doubling up the forms, slide the two parts together to see how they fit. Ideally, the two sections will rest within one another and the bottoms of the triangle will be even. If not make adjustments, just a little bit at a time. Don't be impatient. It's always easier to make small adjustments than to struggle in the end with an opening that's too large. The tree won't stand well if the two sides flop about so don't rush and cut too hastily.
Now's the time to create the cloth that will cover your tree. Pull out your scraps and decorate at will. The trees can be as simple or fancy as you'd like. You can cut the cloth to size or make approximate tree shapes and fine tune it later. Just remember not to decorate or embroider along the center line of the form where the forms need to slide together.
When you've finished decorating the tree cloth, fuse it to one side of each of the four forms and stitch around the edges. In my sample, I used a variegated thread for the body of the tree and a matching thread for the trunk. Trim the cloth if necessary.
On each form, carefully cut the cloth to reveal the slit, making little adjustments at a time. This is why sharp scissors are a must! Go back and stitch around the edges of the slit to secure the cut edges.
Using matte medium or glue, adhere the two matching "bottom up" forms together and the two "top down" forms together. (I prefer matte medium because it's easier for me to spread evenly.) The decorated cloth should be on the outside of the tree form sandwich. The doubled forms now have the sturdiness to make it possible for the tree stand upright. It's best to give the medium time to dry, so lay the tree forms on a protected work surface and put a book -- or something similarly flat and heavy -- on top of them to help the bonding process and keep the forms flat.
Paint the edges in a coordinating or contrasting color to finish the edges. Once dry, fit the forms together.
Viola! Now you have a whimsical tree that stands at your table or on your mantel. You might want to stitch a hanging thread through the top of the tree to create an ornament.
BONUS: You can use this construction concept for any number of simple forms, such as a five point star. Can't you just see a collection of stars as the centerpiece for a 4th of July gathering?