Bitbucket Pull Request Builder Configuration Jenkins
You can install 'Bitbucket Server Webhook to Jenkins' in Bitbucket. 
https://marketplace.atlassian.com/plugins/com.nerdwin15.stash-stash-webhook-jenkins/server/overview

Once install you will need to enable the 'Post Receive' Hook on the required repository.

Remember to enable 'poll SCM' for the Jenkins Job.

Update
You can test the configuration of the plugin here: