No, left biased will also produce 5 splitting operations maximum..
U are saying left bias will split 3 times as you have taken some special set of sorted inputs like 1,2,3,4,5,6,7,8,9,10 i guess,
But try this input combination 10,20,30,40,28,29,26,27,24,25 and perform left biased splitting on it.. U will get maximum splitting as 5