Code copied from Md. Marufuzzaman.
TreeNode treeNodeRoot = new TreeNode(ObjGlobal.ServerIP + " " + ObjGlobal.Port, "S", "~/App_Themes/SQL/Images/DBServer.png", "Default.aspx", "");
this.tvSQLServer.Nodes.Add(treeNodeRoot);
TreeNode treeNodeBranches = new TreeNode("Database", "C", "~/App_Themes/SQL/Images/Folder.png", "Default.aspx", "");
treeNodeRoot.ChildNodes.Add(treeNodeBranches);