Trigger of button is not working in behind code on WPF

Question

There are 2 part for setting style of button.

The 1st is BackgroundProperty by Style.Setters . It's working well.

The 2nd is BackgroundProperty by Style.Triggers which is run by that Mouse is over a button. But, It's not working .

// the 1st BackgroundProperty by Style.Setters
Style style = new Style(typeof(Button));
style.Setters.Add(new Setter(Button.BackgroundProperty, imageSourceOn));

// the 2nd BackgroundPropert by Style.Triggers
Setter setter = new Setter();
setter.Property = Button.BackgroundProperty;
setter.Value = imageSourceOff;
Trigger trigger = new Trigger();
trigger.Property = IsMouseOverProperty;
trigger.Value = true;
trigger.Setters.Add(setter);
style.Triggers.Add(trigger);

Button button = new Button();
button.Margin = new Thickness(0, 5, 80, 5);
button.BorderThickness = new Thickness(0);
button.Name = name;
button.Click += handler;
button.VerticalContentAlignment = VerticalAlignment.Bottom;

// setting Style
button.Style = style;
return button;

Answer 1

Thanks Ed Plunkett. I added ControlTemplate to override the control's background brush property.

Style style = new Style(typeof(Button));
style.Setters.Add(new Setter(Button.BackgroundProperty, imageSourceOn));

This is the ControlTemplate part what I add:

ControlTemplate template = new ControlTemplate(typeof(Button));
FrameworkElementFactory elemFactory = new FrameworkElementFactory(typeof(Border));
elemFactory.Name = "Border";
elemFactory.SetValue(Border.BackgroundProperty, new TemplateBindingExtension(Button.BackgroundProperty));
template.VisualTree = elemFactory;
elemFactory.AppendChild(new FrameworkElementFactory(typeof(ContentPresenter)));

And, It is trigger part.

Setter setter = new Setter();
setter.Property = Button.BackgroundProperty;
setter.Value = imageSourceOff;
Trigger trigger = new Trigger();
trigger.Property = IsMouseOverProperty;
trigger.Value = true;
trigger.Setters.Add(setter);

Finally, I set my ControlTemplate .

template.Triggers.Add(trigger);
setter = new Setter();
setter.Property = Button.TemplateProperty;
setter.Value = template;
style.Setters.Add(setter);

It works well.