I just need a simple modification of the layout available here http://mbostock.github.io/d3/talk/20111116/force-collapsible.html
The above visualization starts with all the nodes being expanded and so the user can visualize the complete hierarchy. The only problem is if the graph is dense, and the hairball that is formed is meaningless.
I would be interested in starting with just the root node and gradually expanding all the nodes as needed. Is it feasible? How much code change is needed?