<nav>
   <nav>
     <ul>
       <li id="al">American League
         <ul>
           <li id="ale">East
             <ul>
               <li>Baltimore Orioles
               </li>
               <li>Boston Red Sox
               </li>
               <li>New York Yankees
               </li>
               <li>Toronto Blue Jays
               </li>
               <li>Tampa Bay Rays
               </li>             </ul>
           </li>
           <li id="alc">Central
             <ul>
               <li>Chicago White Sox
               </li>
               <li>Cleveland Indians
               </li>
               <li>Detroit Tigers
               </li>
               <li>Kansas City Royals
               </li>
               <li>Minnesota Twins
               </li>             </ul>
           </li>
           <li id="alw">West
             <ul>
               <li>Houston Astros
               </li>
               <li>Los Angeles Angels
               </li>
               <li>Oakland Athletics
               </li>
               <li>Seattle Mariners
               </li>
               <li>Texas Rangers
               </li>             </ul>
           </li>         </ul>
       </li>
       <li id="nl">National League
         <ul>
           <li id="nle">East
             <ul>
               <li>Atlanta Braves
               </li>
               <li>Miami Marlins
               </li>
               <li>New York Mets
               </li>
               <li>Philadelphia Phillies
               </li>
               <li>Washington Nationals
               </li>             </ul>
           </li>
           <li id="nlc">Central
             <ul>
               <li>Chicago Cubs
               </li>
               <li>Cincinnati Reds
               </li>
               <li>Milwaukee Brewers
               </li>
               <li>Pittsburgh Pirates
               </li>
               <li>St. Louis Cardinals
               </li>             </ul>
           </li>
           <li id="nlw">West
             <ul>
               <li>Arizona Diamondbacks
               </li>
               <li>Colorado Rockies
               </li>
               <li>Los Angeles Dodgers
               </li>
               <li>San Diego Padres
               </li>
               <li>San Francisco Giants
               </li>             </ul>
           </li>         </ul>
       </li>     </ul>   </nav> </nav>

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

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