VSPackage development, few question about text editor.

I'm working on my own vspackage using C# that target on C++ project.

1.How to add #include file to a header/source file?

2.How do I get filter/folder in a C++ project and add item to filter/folder?

Currently, I can use AddItem function to add files to my project, but files always added to the root of my project, I want to add file to a specified folder/filter like "Common\Assets\xxx.png";

proj.AddItem(VSConstants.VSITEMID_ROOT, VSADDITEMOPERATION.VSADDITEMOP_OPENFILE, fileName, 2, files, IntPtr.Zero, result);

Please help me, thanks.