code: function _new_node_at(bnode, level){
  
  	ll("adding " + bnode.id() + " at level " + level + "!");
  
  	// Create new vertex and add to set.
  	var new_vertex = new bbop.layout.sugiyama.simple_vertex(bnode.id());
  	new_vertex.level = level;
  	vertex_set[ new_vertex.id() ] = new_vertex;
  	
  	// Check the node in to the 'seen' references.
  	first_seen_reference[ new_vertex.id() ] = level;
  	last_seen_reference[ new_vertex.id() ] = level;		 
      }
docs: Add a new node to the global variables.