This is what I came up with.
And, this is how to do it.
1) Gather materials: 3 pieces of felt (found at the craft store for 4 for $1), scissors, tacky glue, and binder clips (optional).
2) Use one piece of felt and make a cone shape starting from one of the corners.
3) Glue the edge down and then cut the bottom (sort of like a semi-circle) so the 'cone' will stand up evenly.
4) Place binder clips over the area you just glued together to help it adhere. (This step might be unecessary, but I found that the felt didn't really stick together with the tacky glue unless forced.) Let your trees sit about 10 minutes before taking the clips off.
5) Repeat steps 2-4 with three different sized cones. (I was able to make all of my cone shapes out of one piece of felt.)
6) Decorate your trees however you'd like! The good thing about this project is that you don't have to glue down any of the decorations on your trees because the felt pieces stick to one another! So you can redecorate your trees as often as you'd like!
As a side note, I created the spiral design by drawing a circle on the felt (about the size of a cd) and cutting it into a spiral. This makes it very easy to drape the spirals over the cones.
I created the 'bunting tree' by making anther spiral out of a circle and cutting little triangles out of the green felt. I found it helpful to use a little dab of glue on the triangles to keep them in place. And, the smallest tree was created simply by cutting small circles out of the felt (pretty obvious, but I didn't want to leave the little guy unmentioned!)
And here's our (sad excuse for a) mantle with felt trees and a little bunting piece I made with the extra felt and an empty frame I had laying around.