The parts of the 11 X 14 tray ladder, which I bought from Porters several years ago, just slip together; I don't think there's a way to attach a second one. My new 16 X 20 tray ladder is scheduled to be delivered tomorrow, so I'm not sure about that. Since I'll use it on top of a three shelf cart, I don't think I'd need any more tray space.
Here's a link to the 16 X 20 model on the Calumet website, the 11 X 14 model is also shown:
I don't really mean to advertise Calumet, but no place else seems to show these; not even the Leedal website.