$siteURL="http://serverName:1111/"
$site=Get-SPSite $siteURL
$web=$site.RootWeb
$list=$web.Lists.TryGetList("cl")
$field=$list.Fields["Country"]
$listNavSettings=[Microsoft.Office.DocumentManagement.MetadataNavigation.MetadataNavigationSettings]::GetMetadataNavigationSettings($list)
$mdnNavHierarchy=New-Object Microsoft.Office.DocumentManagement.MetadataNavigation.MetadataNavigationHierarchy($field)
$listNavSettings.AddConfiguredHierarchy($mdnNavHierarchy)
[Microsoft.Office.DocumentManagement.MetadataNavigation.MetadataNavigationSettings]::SetMetadataNavigationSettings($list, $listNavSettings, $true) |