I have been looking at a few of mine, and I think if you only have the XSD you may have to go back to basics -- the root tag has no REQUIRED identifying mark -- it is the only element tag that is neither a simple element nor contained within another complex element.
So use old-fashioned W3C DOM and parse your XSD as normal XML, then walk the tree and build a Map of all the element names, then walk the tree again and delete from the map:
-- all simple elements
-- all elements that occur inside another element.
You should be left with one element in your Map ...