I have this main wpf window

and this WPF page
You can add user controls to the TabControl. So go to the add new items and select the user control and make what you want (like what you have in the page). Then add an instance of that user control to the TabControl.
protected override void OnRender(DrawingContext drawingContext)
{
if (ISFirstRender)
{
TabItem tabitem = new TabItem();
tabitem.Header = "Tab 3";
pan1.Items.Add(tabitem);
MyUserControl userControl = new MyUserControl();
tabitem.Content = userControl;
ISFirstRender = false;
}
base.OnRender(drawingContext);
}