swift firebase how to set/add data at the top of database

I am building an app that incorporates Firebase and need to be able to be able to add/and or set data at the top of the my database. Currently whenever I add data it places it randomly under the parent node. I've seen some Objective C answers to this but they haven't really made to much sense. Sorry for the lack of code, but I don't know where exactly where to start on this issue. Any help would be great!