Convert List into DataTable using C# in ASP.Net

I tried to convert a List into a DataTable but the DataTable wont store the item inside the List.

C#

protected void RetrieveGL()
{
    List<Retrieve> retrieveList = this.GetGLType();
    DataTable dataTable = ConvertRetrieveListToDataTable(retrieveList);

    GridViewSelection.DataSource = dataTable;
    GridViewSelection.DataBind();
}
private List<Retrieve> GetGLType()
{
    string QueryGLType = "SELECT * FROM BOS_M_TRADER_GL WHERE TDR_CODE = :TDR_CODE";

    using (OracleCommand cmd = new OracleCommand(QueryGLType, con))
    {
        cmd.Parameters.Add("TDR_CODE", OracleDbType.Varchar2).Value = DropDownListTDRCode.SelectedValue;

        using (OracleDataReader odr = cmd.ExecuteReader())
        {
            while (odr.Read())
            {
                retrieve.Add(new Retrieve
                {
                    GLType = odr["GL_TYPE"].ToString(),
                    GLAccNo = odr["GL_ACCNO"].ToString()
                });
            }
        }
        return retrieve;
    }
}
private DataTable ConvertRetrieveListToDataTable(List<Retrieve> retrieveList)
{
    DataTable dataTable = new DataTable();
    dataTable.Columns.Add("GLType", typeof(string));
    dataTable.Columns.Add("GLAccNo", typeof(string));

    foreach (Retrieve item in retrieveList)
    {
        DataRow row = dataTable.NewRow();
        row["GLType"] = item.GLType;
        row["GLAccNo"] = item.GLAccNo;
        dataTable.Rows.Add(row);
    }
    return dataTable;
}

I managed to fetch the data from database and store it inside a list, and then from the list, I tried to store it inside the DataTable. It managed to get into 

row["GLType"] = item.GLType;
row["GLAccNo"] = item.GLAccNo;