Personally I almost never give my rabbits treats on a regular basis, aside from the odd tiny piece of banana or a blueberry every once in a while. I’ve found that fruit does more harm than good with mine (fun to give them, but often goes along with excess cecals)
I like to just use the plain old rabbit pellets as their “treats”, since they are on such a strict ration of them they do see them as treats, or a piece of fragrant basil, mint, or lavendar.
Remember that wild rabbits are strict herbivores, which means their digestive tract is evolved to process mostly low calorie roughage (high fiber, low energy content). With too many treats they tend to not eat as much hay, which is really the most important part of the diet.
I guess this is a long-winded way of saying, “less is more” with treats! Prob best reserved for soothing grumpy bunnies after particularly traumatic events, like nail trims. 
.
.
.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.