Banyan? If so they are aerial roots, you're not going to get them by sticking the tip of the branches into the ground. You need a lot of humidity for aerial roots to develop on their own. You can create them artificially by either making a cut in the branch and inserting it in a tube with soil so the roots grow down into the ground, exposing them as they get thicker (kinda like when you make root over rock or exposed root bonsais), or by approach grafting skinny shoots from the ground into the branches, cutting off the reminder of the shoot once established.