public void createNodes(OpdrachtCatalogus opdrachtCatalogus){
		top.removeAllChildren();
		try {		
			DefaultMutableTreeNode opdracht = null;
			List<Opdracht> opdrachten = opdrachtCatalogus.getOpdrachten();
			for(Opdracht o : opdrachten){
				String nameOpdracht = o.toString();
		
				opdracht = new DefaultMutableTreeNode(nameOpdracht);
				top.add(opdracht);
			}
			
			DefaultMutableTreeNode currentNode = top.getNextNode();
		    do {
		       if (currentNode.getLevel()==1) 
		            tree.expandPath(new TreePath(currentNode.getPath()));
		       currentNode = currentNode.getNextNode();
		       }
		    while (currentNode != null);
			
		} catch (Exception e) {
			System.out.println(e.getMessage());
		}
	}