Владелец окна, чтобы tabitem в на элемент управления TabControl

I created a new window (Project->Add WPf Window)
I can't see it on page 2 (as a parent)

is displayed, but not where I would like it 

in C# it's easy to create Parent, in Wpf I don't understand which one to use between Owner, Parent, Child

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp1"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <DockPanel HorizontalAlignment="Left" Height="411" LastChildFill="False" Margin="0,0,0,0" VerticalAlignment="Top" Width="782" RenderTransformOrigin="0.5,0.5" Cursor="Hand" Background="#FF230FE6">
        <StackPanel Orientation="Horizontal" DockPanel.Dock="Bottom" Margin="2,5" Background="#FFAE2608" Height="36">
            <Button Name="btnPreviousTab" Width="70">Prev.</Button>
            <Button Name="btnNextTab" Width="70">Next</Button>
            <Button Name="btnSelectedTab" Width="70">Selected</Button>
        </StackPanel>
        <TabControl Name="tcSample" Width="735">
            <TabItem x:Name="Pagina1" Header="General">
                <Label Content="Test here..." />
            </TabItem>
            <TabItem x:Name="Pagina2" Header="Security" />
            <TabItem x:Name="Pagina3" Header="Details" />
        </TabControl>
    </DockPanel>
</Window>


private void btnSelectedTab_Click(object sender, RoutedEventArgs e)
        {
            Window oWindow = new Window1();
            Pagina2.Content = oWindow.Content;                                   
            oWindow.Show();            
        }