https://www.w3schools.com/css/css_navbar.asp
On the fifth Example, I like to add more menus. I tried few things and couldn't get it through yet. See below:
div id="sidebar">
<ul>
<li><a href="index.php">Home</a></li>
<li><a href="#">Something</a>
<ul>
<li><a href="#">Something More</a>
<ul>
<li><a href="#">More of this #1</a></li>
<li><a href="#">More of this #2</a></li>
<li><a href="#">More of that #3</a></li>
</ul>
</li>
<li><a href="#">Something Even More</a>
<ul>
<li><a href="#">More of this #4</a></li>
<li><a href="#">More of this #5</a></li>
<li><a href="#">More of that #6</a></li>
</ul>
</li>
</ul>
</li>
<li>
<a href="#">Contact me</a>
</li>
</ul>
</div>
As of this, there's only three main menu: Home, Something, Contact me. Then upon hover the Something, two more submenu pop out on the side of Something, just Something More and Something Even More. Then upon mouse hover over the two submenu, another 3 more submenu pops out on the side of the 2nd submenu...