API for modifying "Project Files" node

Hi!

Background: While you can see the complete files via the "Files"
window, I'd like to see other files such as package.json, gulpfile.js,
bower.json, etc in the "Project Files" node of the "Project" window,
and not only pom.xml (Maven projects).

I'm currently developing my first plugin for NetBeans, which is
supposed to add "Additional Important Files" in the "Project Files"
node of the "Project" window. I have a work in progress[1], which adds
files to the "ROOT" of the Project (screenshot[2]). 

Which API should I use to register these files as children of "Project
Files"?


P.S.: Link to an existing impl of this feature I'm looking for is also
appreciated!


[1]
https://github.com/devcsrj/nbm-additionalimportantfiles/blob/master/src
/io/devcsrj/netbeans/plugin/additionalimportantfiles/AdditionalImportan
tFilesNodeFactory.java
[2] http://postimg.org/image/obg1yj76n/