Get xml elements recursive using c#/xpath

I have an xml document looking something like this:

HTML Code:

---

<Menu>
  <Item text="lvl1" Role="A">
    <Item text="lvl2" Role="A">
      <Item text="lvl3" Role="A" />
      <Item text="lvl3" Role="B" />
    </Item>
    <Item text="lvl2" Role="B" />
  </Item>
  <Item text="lvl1" Role="B">
  </Item>
</Menu>

---

I'd like to get all nodes with a specific role. Something like this:

Code:

---

XmlDataSource.XPath = "//Item[contains(@Role, 'A')]"

---

It works on a single level but how do I filter my elements in all levels?