A fine, often starched net of silk, rayon, or nylon, used especially for veils, tutus, or gowns. That's what Tulle is. So I bet that a tulle dress was made out of tulle.
If you are attaching it to the waist of the dress (hopefully there is already a seam to follow!), use thread of a contrasting color to baste it into place, using 1/2 inch hand stitches. Straight pins...