Here are some of the Dash contributions to Bitcoin over the years:
https://github.com/bitcoin/bitcoin/pulls?q=is%3Apr+author%3APastaPastaPasta
https://github.com/bitcoin/bitcoin/pulls?q=is%3Apr+author%3AUdjinM6
https://github.com/bitcoin/bitcoin/pulls?q=is%3Apr+author%3Aknst
https://github.com/bitcoin/bitcoin/issues?q=is%3Aissue+author%3Aknst+is%3Aclosed