Use ShowSiblings property :
<Property Key="ShowSiblings" Value="true"/>
If set the TRUE, the outcome is the same options as the “Display the current site, the navigation items below the current site, and the current site's siblings” option in the user interface (second option from the picture below). Note that the IncludeSubSites and IncludePages parameters also affects to outcome.
This controls the inheritance of the current navigation. If set the true, we would get the same results as by selecting the "Display the same navigation items as the parent site" from the user interface (the first option from the picture below)
<Property Key="InheritCurrentNavigation" Value="true"/>
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