I made these Christmas trees by simply hot gluing pieces of green sea glass to a foam floral cone! If you don't have a huge supply of sea glass, you can buy imitation sea glass at a craft store... although I wouldn't necessarily approve! ;) Use bigger pieces at the bottom (you want flat edges along the bottom) and then work your way around and layer pieces, gradually going smaller. Then decorate your trees as you wish!
These floral cones actually have a flat top, so on the smaller one I just glued pieces of glass together to create a pointed edge. On the taller tree, I added clay to create a point (set with a heat gun then also hot glued to the top) and continued to attach my pieces of glass. If you have the supplies already, I'd recommend the clay method, but don't go out of your way to do it that way.
I love how these trees turned out and will definitely be making more before next Christmas! I want to try one with my white sea glass too.
I hope you all had a wonderful Christmas!