Question

The following code snippetcode has some issue, I don’t know where to place it.

                    <ControlTemplate.Triggers>
                        <Trigger Property="IsExpanded" Value="True">
                            <Setter TargetName="ExpandSite" 
                                          Property="Visibility" 
                                          Value="Visible"/>
                        </Trigger>
                    </ControlTemplate.Triggers>

Answer 1

You have the <ControlTemplate.Triggers> element inside the <Grid> instead of directly inside the <ControlTemplate>. Move it down after the line that has </Grid> and before the line that has </ControlTemplate> so that it is a direct child of the <ControlTemplate> element.