Jenkins Multibranch Pipeline: Differentiate between build triggered by branch indexing vs webhook

Question

I have a Jenkins multibranch pipeline for github and currently it triggers builds whenever a branch is indexed. I have certain actions in my pipeline that I only want triggered whenever there are changes to a branch (on a webhook push). So I was wondering if there's a Jenkins environment variable that will allow me to distinguish between the two different type of builds. Or if there's a git solution to check when the last change was made to the branch and differentiate it that way