Which preposition to use with occasional

bushesfor Occurrences 1%

Pinewoods rely on their undergrowthbracken and whortleberry and occasional bushesfor their spring illuminations, and the whitebeam shone as bright in that wood as a lamp in the dark.

in Occurrences 1%

I had helped him occasional in the beginning,learned him how to veer and haul a brace, let go or belay a sheet,but let him alone generally speaking, and went about my own business.

Which preposition to use with  occasional