> As far as I can see, there is no mention of how many elements are inserted in each run?

FYI it's in the title of the plots.

Ah, I did not see that. Yeah that definitely needs bigger fonts. Or better: Average the runs and perform them with different numbers of items and put those as one axis, instead of wasting an axis for the number of a run. Then we would get a much better idea about how the performance changes with respect to the number of items.