using (SPSite site = new SPSite("http://sharepoint2010"))
{
using (SPWeb web = site.OpenWeb())
{
SPList list = web.Lists.TryGetList("Docs");
SPContentType ct = web.ContentTypes[new SPContentTypeId("0x0120D520")];
var hashTable = new Hashtable();
hashTable.Add("DocumentSetDescription", "test");
DocumentSet documentSet = DocumentSet.Create(list.RootFolder, "test", list.ContentTypes.BestMatch(ct.Id), hashTable,true);
SPFolder folder = documentSet.Folder;
using (FileStream strm = new FileInfo(@"C:\test\test.txt").Open(FileMode.Open))
{
byte[] data = new byte[strm.Length];
strm.Read(data, 0, (int)strm.Length);
folder.Files.Add("test.txt", data);
folder.Update();
}
}
}