def findFileRtiIndex(self, childIndex):
        """ Traverses the tree upwards from the item at childIndex until the tree
            item is found that represents the file the item at childIndex
        """
        parentIndex = childIndex.parent()
        if not parentIndex.isValid():
            return childIndex
        else:
            parentItem = self.getItem(parentIndex)
            childItem = self.getItem(childIndex)
            if parentItem.fileName == childItem.fileName:
                return self.findFileRtiIndex(parentIndex)
            else:
                return childIndex
Traverses the tree upwards from the item at childIndex until the tree
            item is found that represents the file the item at childIndex