Without knowing your hierarchy of paging, you could write a script to copy these rows. If you notice, you could see, for a particular Page, same difference is maintained between ParentPageId and PageId in original record and copied record. You could take advantage of that.
DECLARE @maxpageid INT
SELECT @maxpageid = MAX(PageId) FROM PageList
INSERT INTO PageList (PageId, Name, ParentPageId) SELECT (PageId + @maxpageid), Name,
WHEN 0 THEN 0
ELSE (ParentPageId + @maxpageid)
This is not is correct approach. If this copying is one time and pageIds are +ve integer, then it would work fine. I would recommend to use recursive stored procedure/ sql function to do this.