Create a new treeitem for this reftrack instance.

        .. Note:: Parent should be set, Parent should already have a treeitem.
                  If there is no parent, the root tree item is used as parent for the treeitem.

        :returns: a new treeitem that contains a itemdata with the reftrack instanec.
        :rtype: :class:`TreeItem`
        :raises: None

def create_treeitem(self, ):
        """Create a new treeitem for this reftrack instance.

        .. Note:: Parent should be set, Parent should already have a treeitem.
                  If there is no parent, the root tree item is used as parent for the treeitem.

        :returns: a new treeitem that contains a itemdata with the reftrack instanec.
        :rtype: :class:`TreeItem`
        :raises: None
        """
        p = self.get_parent()
        root = self.get_root()
        if p:
            pitem = p.get_treeitem()
        else:
            pitem = root.get_rootitem()
        idata = root.create_itemdata(self)
        item = TreeItem(idata, parent=pitem)
        return item