display: none

Example 6.2 - display: none; - Example 6.2 (Without Styles)
 
 <nav>
   <ul>
     <li>American League
       <ul>
         <li id="ale">East
           <ul>
             <li>Baltimore
             </li>
             <li>Boston
             </li>
             <li>New York
             </li>
             <li>Toronto
             </li>
             <li>Tampa Bay
             </li>           </ul>
         </li>
         <li id="alc">Central
           <ul>
             <li>Chicago
             </li>
             <li>Cleveland
             </li>
             <li>Detroit
             </li>
             <li>Kansas City
             </li>
             <li>Minnesota
             </li>           </ul>
         </li>
         <li id="alw">West
           <ul>
             <li>Houston
             </li>
             <li>Los Angeles
             </li>
             <li>Oakland
             </li>
             <li>Texas
             </li>
             <li>Seattle
             </li>           </ul>
         </li>       </ul>
     </li>   </ul> </nav>

In style element (<style>) within head element:


#ale ul { display: none; }
#alw ul { display: none; }
 

display

Full list for the American League:
display