也许是这样的：

使用 UNION

var t= Enumerable
         .Range(0,1)
         .Select (e =>
                    new{employeeid=0,employeeName="Select"})
       .Union(
          db.tblemployee
          .Select (u =>
                   new {employeeid=u.employeeid,employeeName=u.employeeName} ));

使用 UNION ALL

var t= Enumerable
         .Range(0,1)
         .Select (e =>
                    new{employeeid=0,employeeName="Select"})
       .Concat(
          db.tblemployee
          .Select (u =>
                   new {employeeid=u.employeeid,employeeName=u.employeeName} ));

其中db是数据上下文