Funny, I also use a tomato cage for a tabletop Christmas tree, but I use live greenery to make the tree. Place the tomato cage upside down as you did on a large catering disposable tray. Place several blocks of wet oasis - one on top of each other and run through with thick wire (coat hanger wire will do) attaching the top of the wire to the top of the tomato cage so they stay in place. Start filling in with assorted green branches - in this one I used mock orange, silver dollar eucalyptus, the green stem and leaves of a common wild terrestial orchid and then decorated with red anthuriums. When I lived on the mainland, I decorated these trees with red carnations or red roses and baby's breath inserted in florist tubes.