Kongnamul (soy bean sprout) roots?

Generally sprouts are sold before they form a tap root, as they use up the energy stored in the seed to produce the sprout. You could try either sprouting your own and letting them grow longer, but they are likely to rot instead of forming roots, if they are not in the sun. You could put sprouts with water in the sun, they will start to grow just like any other plant. But we don’t usually eat bean leaves because they are bitter.