[jQuery] Problem traversing up list

[ximo wallas]

Hello there, after too much sarching I have almost give it up with the 
following.
I have a list with another list nested:
<ul>
    <li id="item1">Item 1
      <ul>
        <li id="item1-1">
          Item 1 - 1
        </li>
        <li id="item1-2">

          Item 1 - 2

        </li>
      </ul>
    </li>
</ul>
Let's say I know the ID of "item1-2" or "item1-1" how can I get the id of the 
li (item1)?
I have tried with:
alert($('#item1-1').parentNode().id) 
But it gaves me an error, maybe just because it is an aberration...