How to merge columns in C# Windows Forms

Question

This is the datagridview that I have current dgview

But I want to merge columns in the gridview so it looks like in this screenshot:

My code:

foreach (DataRow row in dt.Rows)
{
    dgc[i] = new DataGridViewTextBoxColumn();
    dgc[i].HeaderText = row["account_name"].ToString();
    dataGridView1.Columns.Add(dgc[i]);

    i++;
}