Help allows both a plain infinitival complement and a to-infinitival complement. The -ing clause as complement is marginally acceptable at best.
In the Corpus of Contemporary American English the results for 'he helped...' are as follows:
- plain infinitival 329
- to-infinitival 232
- -ing clause 2
Only one of the -ing clause examples could actually be argued as a complement to help.
Snape's logic and deductive reasoning skills were such that he helped protecting the Philosopher's Stone by creating an obstacle (Harry Potter Wiki)
The Cambridge Grammar of the English Language has help on p1229 as a allowing to-infinitivals and bare infinitivals, but not gerund-participials (-ing clauses).
Then again, ngrams gives 'help adding' as quite a common colocation, more so even than 'help add' or 'help to add':
However, most of these hits are not in prose, but rather titles or links along the lines of 'Help Adding Underscore At End of Number'.