WPF

<Window x:Class="SimpleWpfTabTest.Window1"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  Title="Window1" Height="300" Width="300">
  <Grid>
  <Grid.RowDefinitions>
    <RowDefinition Height="Auto"/>
    <RowDefinition Height="20" />
  </Grid.RowDefinitions>
  <TabControl Name="myTab" Grid.Row="0">
  </TabControl>
  <Button Name="btnAddTab" Grid.Row="1" Click="btnAddTab_Click" />
  </Grid>
</Window>

private void btnAddTab_Click(object sender, RoutedEventArgs e)
{
  // Create a TabItem
  TabItem child = new TabItem{Name="childTab" + myTab.Items.Count.ToString(), Header="Added"};
  // The TabItem needs a content holder - I'm using a StackPanel
  StackPanel childPanel = new StackPanel();
  child.Content = childPanel;
  // The button will be added as a child of the stack panel.
  Button myButton = new Button { Name = "hello", Content = "Woopee" };
  childPanel.Children.Add(myButton);
  // Add the TabItem to the tab
  myTab.Items.Add(child);
  // And set the focus to it.
  child.Focus();
}