Param
(
    [string]$DistinguishedName,
    [string]$UserIdentity = "",
    [array]$Groups = @(),
    [switch]$Duplicates
)

if ($UserIdentity -notin @($null, "")){
    $DistinguishedName = (Get-ADUser -Identity $UserIdentity).distinguishedname
}

#The user to check.
# $User = "max.mustermann@domain.com";
 
#Get all groups.
# $Groups = Get-ADUserNestedGroups -DistinguishedName (Get-ADUser -Identity $User).DistinguishedName;

#Output all groups.
# $Groups | Select-Object Name | Sort-Object -Property Name;

#Get the AD object, and get group membership.
$ADObject = Get-ADObject -Filter "DistinguishedName -eq '$DistinguishedName'" -Properties memberOf, DistinguishedName;

#If object exists.
If($ADObject)
{
    #Enummurate through each of the groups.
    Foreach($GroupDistinguishedName in $ADObject.memberOf)
    {
        #Get member of groups from the enummerated group.
        $CurrentGroup = Get-ADObject -Filter "DistinguishedName -eq '$GroupDistinguishedName'" -Properties memberOf, DistinguishedName;
    
        #Check if the group is already in the array.
        If(($Groups | Where-Object {$_.DistinguishedName -eq $GroupDistinguishedName}).Count -eq 0)
        {
            #Add group to array.
            $Groups +=  [PSCustomObject]@{
                DistinguishedName=$CurrentGroup.DistinguishedName
                Name=$CurrentGroup.Name
                ObjectClass=$CurrentGroup.ObjectClass
                Parent=$DistinguishedName
            };

            #Get recursive groups.      
            $Groups = &$PSCommandPath -DistinguishedName $GroupDistinguishedName -Groups $Groups;
        } elseif ($Duplicates) {
            "Duplicate: $($CurrentGroup.DistinguishedName)" | Out-Host
        }
    }
}

#Return groups.
$Groups;