public class DataItem
{
  public int ID { get; set; }
  public DataSubItem SubItems { get; set; }
  
  public DataItem(int id, DataSubItem subitem) { ID = id; SubItems = subitem; }
}

public class DataSubItem
{
  public string Text1 { get; set; }
  public string Text2 { get; set; }

  public DataSubItem(string text1, string text2) { Text1 = text1; Text2 = text2; }
}

private void Window_Loaded(object sender, RoutedEventArgs e)
{
  ObservableCollection<DataItem> list = new ObservableCollection<DataItem>();

  DataItem item = null;
  list.Add(new DataItem(1, new DataSubItem("aaa1", "bbb1")));
  list.Add(new DataItem(2, new DataSubItem("aaa2", "bbb2")));

  grid1.ItemsSource = list;
  grid2.ItemsSource = list;
}

<Window x:Class="wpf2.Window2"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window2" Height="258" Width="643" Loaded="Window_Loaded">
	<Grid>
		<Grid.RowDefinitions>
			<RowDefinition />
			<RowDefinition />
		</Grid.RowDefinitions>

		<DataGrid Grid.Row="0" Name="grid1" AutoGenerateColumns="False">
			<DataGrid.Columns>
				<DataGridTextColumn Binding="{Binding ID}" />
				<DataGridTextColumn Binding="{Binding SubItems.Text1}" />
			</DataGrid.Columns>
		</DataGrid>

		<DataGrid Grid.Row="1" Name="grid2" AutoGenerateColumns="False">
			<DataGrid.Columns>
				<DataGridTextColumn Binding="{Binding ID}" />
				<DataGridTextColumn Binding="{Binding SubItems.Text2}" />
			</DataGrid.Columns>
		</DataGrid>

	</Grid>
</Window>