How Should You Modify the Following Code So It Passes

How should you modify the following code so it passes the W3C's HTML validation service?
Wild, Cheryl Strayed
<ul>
<li>Chapter 1: The Ten Thousand Things</li>
<ul>
<li>Mayo Clinic</li>
<li>Dreams</li>
</ul>
<li>Chapter 2: Splitting</li>
...
</ul>