The base of my dragon tree doesn't seem to grow, it looks like his branches are just growing out of the ground. <p>
Have you tried removing any soil from around the trunks, or are there roots just below the soil? In other words, is it planted much too deeply to begin with? If not, how much sun does it get? They can take quite a bit all day, but don't like to be watered until they're more dry than wet.
I honestly don't think they're supposed to grow at the base. My experience with these plants is that they eventually become more tree-like. They will continue to grow from the top while losing leaves at the base to create a trunk. My aunt has several that are at least 5 feet tall now. The larger ones have eventually split off and created some offshoots. The trunks are no larger than the bases of the plants shown in your picture and they'll eventually need some support. My Dragon tree looks just like yours and is slowly getting taller. Hope this helps, Amy