Hi,

You shouldn't place a XamMenuItem in your ItemTemplate. A XamMenuItem will be created as a container for the DataTemplate you provide, which means you'll end up having XamMenuItem inside a XamMenuItem. So, you'll have a XamMenuItem with MenuOrientation set to "Horizontal" inside of another XamMenuItem, generated as a container to host the one you specified in your  DataTemplate. And the Parent one will have it's MenuOrientation set to the default value (which is Vertical). Instead, you could specify a DefaultItemsContainer, which will be used when generating the container items.

So your code should look something like this:

        <ig:XamMenu x:Name="igMenu" Height="30" Margin="10" ItemsSource="{StaticResource data}">
            <ig:XamMenu.DefaultItemsContainer>
                <DataTemplate>
                    <ig:XamMenuItem MenuOrientation="Horizontal" />
                </DataTemplate>
            </ig:XamMenu.DefaultItemsContainer>
            
            <ig:XamMenu.HierarchicalItemTemplate>
                <ig:HierarchicalDataTemplate ItemsSource="{Binding Path=Children}">
                    <ig:HierarchicalDataTemplate.DefaultItemsContainer>
                        <DataTemplate>
                            <ig:XamMenuItem NavigationOnClick="True"
                                            MenuOrientation="Horizontal"
                                            NavigationUri="{Binding PageURL}"
                                            NavigationElement="{Binding ElementName=menuFrame}"
                                            StaysOpenOnClick="True">
                            </ig:XamMenuItem>
                        </DataTemplate>                      
                    </ig:HierarchicalDataTemplate.DefaultItemsContainer>
                    
                    <ig:HierarchicalDataTemplate.ItemTemplate>
                        <DataTemplate>
                            <TextBlock Text="{Binding Name}" />
                        </DataTemplate>
                    </ig:HierarchicalDataTemplate.ItemTemplate>                    
                    
                    <DataTemplate>
                        <TextBlock Text="{Binding Name}" />
                    </DataTemplate>
                </ig:HierarchicalDataTemplate>
            </ig:XamMenu.HierarchicalItemTemplate>
        </ig:XamMenu>

Hope this helps,