Adding files to EnvDTE80.solution

I have used  EnvDTE80.Solution for creating the solution folder in the existing solution.

While adding the files to these solution folder by c# codeing, the files get opened automatically.

solutionFolder.ProjectItems.AddFromFile("filePath");

I dont want to open such files.. how to suppress that.

I need simply to add files to that folder.. how to do it..

Thanks in advance