How to properly bind objects using reportviewer?

I recently studied a report viewer, and I have one problem that I cannot solve ...

I am trying to bind data from a collection of objects (headers), where each object has a set of child objects (rows). How can this be done? Below are the code snippets that I have (somedata is a collection of header objects).

A Windows form with a ReportViewer control has the following meanings:

reportViewer1.ProcessingMode = ProcessingMode.Local;
reportViewer1.LocalReport.LoadReportDefinition(GetReport());
reportViewer1.LocalReport.DataSources.Clear();
var dataSourcesNames = GetDataSourceNames();
var headerSource = new ReportDataSource(dataSourcesNames[0], somedata);
reportViewer1.LocalReport.DataSources.Add(headerSource);
reportViewer1.RefreshReport();

Header Object:

public class ReportHeader{
    readonly string id;
    readonly List<ReportRow> rows;

    public ReportData(Header h) {
        this.id = h.Id;
        rows = new List<ReportRow>();
        foreach(RowObject o in h.Rows){
            rows.Add(new ReportRow(o));
        }
    }

    public string Id { get { return id; } }
    public List<ReportRow> Rows { get { return rows;} }
}

String object:

public class ReportRow{
    readonly decimal sum;
    readonly string type;
    readonly string code;

    public ReportDataRow(RowObject r) {
        sum = r.Sum;
        type = r.Type;
        code = r.Code;
    }

    public decimal Sum { get { return sum; } }
    public string Type { get { return type; } }
    public string Code { get { return code; } }
}

I created a report that has all ReportHeader properties and a list that should contain all ReportRows, but it does not work. The only solution was to create two separate collections, the ReportHeader collection and the ReportRow collection, and then bind them separately, as shown below:

var headerSource = new ReportDataSource(dataSourcesNames[0], somedata);
reportViewer1.LocalReport.DataSources.Add(headerSource);
var rowSource = new ReportDataSource(dataSourcesNames[1], somedata.Rows);
reportViewer1.LocalReport.DataSources.Add(rowSource);

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