tree for ChilNode of childNode in javascript

i have this simple html:

<div id="tree">
     <div class="roi">
         <ul>
             <li>text1</li>
             <li>text2</li>
             <li>text3
                 <ul>
                     <li>insideText1<li>
                     <li>insideText2<li>
                 </ul>
             </li>
         </ul>
     </div>
 </div>
 

i want to get only the item "text2" and the item "insideText2";
so i tried to wrote:

var Tree=document.getElementById("tree").document.getElementsByTagName("UL");

But i do'not know how to rich the specific li that conatins :"text2" and "insideText2".
Please help.
Thanks.

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