Enchantement level max on Enchanting table HELP

Hi, 

I would like to create an enchantment similar to sharpness. However, sharpness like many other enchantments is available at level 5 only by combining two sharpnesses at level 4.

 I don't know how to add an enchantment whose max level is 5, as Mcretor does not generate it in the enchantment tables but only in the chests of structures, and that it can be obtained by combining two level 4 items.