Add Farm Solution in Sharepoint

//Main

 FileStream stream = null;

       
            string UploadFileName = @"C:\sample.wsp";


            FileInfo fileInfo = new FileInfo(UploadFileName);

            //Verifying the condition whether that file is existed (or) not
            if (!fileInfo.Exists) { throw new InvalidOperationException("The file does not exist."); }

            byte[] bytes = System.IO.File.ReadAllBytes(fileInfo.Name);

            //If file existed converting it in to the stream to transfer
            stream = File.OpenRead(UploadFileName);
            stream.Position = 0;

//usage

AddSolutionWorker("sample.wsp",bytes)

//Method

  public void AddSolutionWorker(string wspName, byte[] wspcontents)
  {
   string tdir = Path.GetDirectoryName(Path.GetTempFileName());
   string wsppath = string.Format(@"{0}\{1}", tdir, wspName);

   if (File.Exists(wsppath))
    File.Delete(wsppath);

   File.WriteAllBytes(wsppath, wspcontents);

   SPFarm.Local.Solutions.Add(wsppath);

   File.Delete(wsppath);
  }