code: private void createNodes(DefaultMutableTreeNode top) {
  
      // categories
      DefaultMutableTreeNode category = null;
      // leaves
      DefaultMutableTreeNode defaultMutableTreeNode = null;
  
      // PCB Files
      category = new DefaultMutableTreeNode("PCB Images");
      top.add(category);
  
      long count = PCBDAO.selectCount();
      for (int i = 1; i <= count; i++) {
        PCB pcb = PCBDAO.selectSingle(i);
        defaultMutableTreeNode = new DefaultMutableTreeNode(pcb);
        category.add(defaultMutableTreeNode);
      }
    }
docs: Create the tree
  
  @param top