Realtime Database trigger cloud function

I would like to index the information modified:

exports.indexInformationTitle = functions.database.ref('/users/{userID}/information/shopName')
.onWrite(event => {
  const title = event.data.val();
  return event.data.ref.parent.child('index/title/' + title[0]).push(string);
});

But I want to save the information on a different parent directory using 'push' function.

via Isaiah Jan Caracol Navasquez