Display the tree structure data of Class Diagram 1 into the drop-down box form of Figure 2. Optgroup seems to be unable to meet the requirements of more than two levels.
业精于勤，荒于嬉;行成于思，毁于随。
Waiting online................
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
Waiting online................