See the code below, that shows how to fill FlyGrid with data and separators:
[C#]
private void FillGrid(FlyGrid flyGrid)
{
  for(int i=0; i < 10; i++)
  {
    //create separator with title "Row#"
    SeparatorNode sepNode = new SeparatorNode("Row#" + i.ToString());
    //add children
     for(int j=0; j < 5; j++)
    {
      //create data of node, cells contents
      object[] data = new object[]{"ChildRow of"+ i.ToString, "Child#" + j.ToString()};
      //create child
      Node newNode = new Node(data);
      //add to the separator node
      sepNode.Items.Add(newNode);
    }
    //add separator
    flyGrid.Rows.Items.Add(sepNode)
  }
}