How can I create relations in LINQ

SqlConnection con1 = new SqlConnection(con);

SqlDataAdapter dadCats = new SqlDataAdapter("select  menuid,menuname,imageurl,parentmenuid from  menus where menutype= 'mainmenu' and  menulevel='0' and menuid='5'", con1);

SqlDataAdapter dadCats1 = new SqlDataAdapter("select menuid,menuname, parentmenuid,urlname,imageurl from  menus where menutype= 'submenu' and menulevel='1' and parentmenuid='5'", con1);

SqlDataAdapter dadCats2 = new SqlDataAdapter("select menuid,menuname, parentmenuid,urlname,imageurl from  menus where menutype= 'submenu' and menulevel='2'and parentmenuid in(6,7,8,9,10)", con1);
DataSet dst = new DataSet();

dadCats.Fill(dst, "Menu");
dadCats1.Fill(dst, "Menu1");
dadCats2.Fill(dst, "Menu2");

dst.Relations.Add("Children", dst.Tables["Menu"].Columns["menuid"], dst.Tables["Menu1"].Columns["parentmenuid"]);
dst.Relations.Add("Children1", dst.Tables["Menu1"].Columns["menuid"], dst.Tables["Menu2"].Columns["parentmenuid"]);