When upgrading pick enchants (like efficiency or fortune etc.) it's fairly tedious to do if you want to apply 5 or 10 levels at a time. I'd be nice to have some sort of bulk apply feature where you can add multiple levels at a time.
To keep the current 1 click is 1 level functionality, it could works as follows:
Open the mana exchange and left click an enchant to just add 1 level.
If you want to add multiple levels you can middle click the enchant and then you get a menu asking for how many levels you want to add. Select the amount of levels and it will (try to) bulk add the levels if you have enough mana.
The right click will still be for disenchanting 1 level (Perhaps even add a bulk disenchant? Might not be that usefull though).