How to replace merge field with chart in Word document using mail merge?

using Syncfusion.DocIO;
using Syncfusion.DocIO.DLS;
using Syncfusion.OfficeChart;

using (FileStream fileStream = new FileStream(Path.GetFullPath(@"../../../Template.docx"), FileMode.Open, FileAccess.ReadWrite))
{
    //Loads an existing Word document into DocIO instance.
    using (WordDocument document = new WordDocument(fileStream, FormatType.Automatic))
    {
        //Gets the employee details as “IEnumerable” collection
        List<Employees> employeeList = GetEmployeeData();
        //Creates an instance of MailMergeDataTable by specifying MailMerge group name and IEnumerable collection.
        MailMergeDataTable dataTable = new MailMergeDataTable("Employees", employeeList);
        //Uses the mail merge event handler to insert chart during mail merge.
        document.MailMerge.MergeField += new MergeFieldEventHandler(MergeField_EmployeeGraph);
        //Performs Mail merge.
        document.MailMerge.ExecuteGroup(dataTable);
        //Unhooks the event after mail merge execution.
        document.MailMerge.MergeField -= new MergeFieldEventHandler(MergeField_EmployeeGraph);
        //Creates file stream.
        using (FileStream outputStream = new FileStream(Path.GetFullPath(@"../../../Result.docx"), FileMode.Create, FileAccess.ReadWrite))
        {
            //Saves the Word document to file stream.
            document.Save(outputStream, FormatType.Docx);
        }
    }
}

private static void MergeField_EmployeeGraph(object sender, MergeFieldEventArgs args)
{
    //Creates chart based on the field value and insert into the Word document.
    if (args.FieldName == "GraphDetails")
    {
        //Gets their owner row.
        WParagraph paragraph = args.CurrentMergeField.OwnerParagraph;
        //Gets the field value.
        List<object[]> graphDetails = args.FieldValue as List<object[]>;
        //Creates the chart.
        WChart chart = CreateChart(paragraph.Document, graphDetails);
        int indexOfField = paragraph.ChildEntities.IndexOf(args.CurrentMergeField);
        //Clears the field;
        args.Text = string.Empty;
        //Inserts the chart at corresponding field location.
        paragraph.ChildEntities.Insert(indexOfField, chart);
    }
}

/// <summary>
/// Gets the employee data to perform mail merge. 
/// </summary>
public static List<Employees> GetEmployeeData()
{
    //Creates graph data for first employee.
    List<object[]> graphDetailsForEmployee1 = new List<object[]>();
    graphDetailsForEmployee1.Add(new object[] { "Month", "Highest Sale", "Average Sale", "Lowest Sale" });
    graphDetailsForEmployee1.Add(new object[] { "September", 67, 55, 12 });
    graphDetailsForEmployee1.Add(new object[] { "October", 74, 71, 70 });
    graphDetailsForEmployee1.Add(new object[] { "November", 81, 74, 60 });
    graphDetailsForEmployee1.Add(new object[] { "December", 96, 71, 20});
 
    //Creates graph data for the second employee.
    List<object[]> graphDetailsForEmployee2 = new List<object[]>();
    graphDetailsForEmployee2.Add(new object[] { "Month", "Highest Sale", "Average Sale", "Lowest Sale" });
    graphDetailsForEmployee2.Add(new object[] { "September", 100, 65, 50 });
    graphDetailsForEmployee2.Add(new object[] { "October", 72, 34, 15 });
    graphDetailsForEmployee2.Add(new object[] { "November", 150, 81, 63 });
    graphDetailsForEmployee2.Add(new object[] { "December", 91, 75, 50 });
 
    //Creates graph data for the third employee.
    List<object[]> graphDetailsForEmployee3 = new List<object[]>();
    graphDetailsForEmployee3.Add(new object[] { "Month", "Highest Sale", "Average Sale", "Lowest Sale" });
    graphDetailsForEmployee3.Add(new object[] { "September", 58, 26, 14 });
    graphDetailsForEmployee3.Add(new object[] { "October", 55, 45, 30 });
    graphDetailsForEmployee3.Add(new object[] { "November", 62, 51, 23 });
    graphDetailsForEmployee3.Add(new object[] { "December", 72, 45, 11 });
 
    //Adds all details in employee data collection for all employees.
    List<Employees> employeeData = new List<Employees>();
    employeeData.Add(new Employees("Nancy", "Davolio", "1", "505 - 20th Ave. E. Apt. 2A,", "Seattle", "USA", graphDetailsForEmployee1));
    employeeData.Add(new Employees("Andrew", "Fuller", "2", "908 W. Capital Way", "Tacoma", "USA", graphDetailsForEmployee2));
    employeeData.Add(new Employees("Margaret", "Peacock", "3", "4110 Old Redmond Rd.", "Redmond", "USA", graphDetailsForEmployee3));
    return employeeData;
}
 
/// <summary>
/// Creates the chart based on the graph data.
/// </summary>
private static WChart CreateChart(WordDocument document, List<object[]> graphDetails)
{
    //Create the new chart.
    WChart chart = new WChart(document);
    chart.Width = 410;
    chart.Height = 250;
    chart.ChartType = OfficeChartType.Column_Clustered;
    //Assign data.
    AddChartData(chart, graphDetails);
    //Set a chart title.
    chart.ChartTitle = "Sales Report";
    //Set Datalabels.
    IOfficeChartSerie serie1 = chart.Series.Add("Highest Sale");
    //Set the data range of chart series – start row, start column, end row and end column.
    serie1.Values = chart.ChartData[2, 2, 5, 2];
    IOfficeChartSerie serie2 = chart.Series.Add("Average Sale");
    //Set the data range of chart series start row, start column, end row and end column.
    serie2.Values = chart.ChartData[2, 3, 5, 3];
    IOfficeChartSerie serie3 = chart.Series.Add("Lowest Sale");
    //Set the data range of chart series start row, start column, end row and end column.
    serie3.Values = chart.ChartData[2, 4, 5, 4];
    //Set the data range of the category axis.
    chart.PrimaryCategoryAxis.CategoryLabels = chart.ChartData[2, 1, 6, 1];
    //Set legend.
    chart.HasLegend = true;
    chart.Legend.Position = OfficeLegendPosition.Bottom;
    //Hiding major gridlines
    chart.PrimaryValueAxis.HasMajorGridLines = false;
    return chart;
}
 
/// <summary>
/// Set the values for the chart.
/// </summary>
private static void AddChartData(WChart chart, List<object[]> graphDetails)
{
    //Set the value for chart data.
    int rowIndex = 1;
    int colIndex = 1;
    //Get the value from the DataTable and set the value for chart data
    foreach (object[] row in graphDetails)
    {
        foreach (object value in row)
        {
            chart.ChartData.SetValue(rowIndex, colIndex, value);
            colIndex++;
            if (colIndex == 5)
            break;
        }
        colIndex = 1;
        rowIndex++;
    }
}
 
/// <summary>
/// Represents a class to maintain employee details.
/// </summary>
public class Employees
{
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string EmployeeID { get; set; }
        public string Address { get; set; }
        public string City { get; set; }    
        public string Country { get; set; }
        public List<object[]> GraphDetails { get; set; }
        public Employees(string firstName, string lastName, string employeeID, string address, string city, string country, List<object[]> graphDetails)
        {
            FirstName = firstName;
            LastName = lastName;
            EmployeeID = employeeID;
            Address = address;
            City = city; 
            Country = country;
            GraphDetails = graphDetails; 
        }
}