src/Security/Get-XrmRootBusinessUnit.ps1

<#
    .SYNOPSIS
    Retrieve root business unit.

    .DESCRIPTION
    Get top business unit of organization.

    .PARAMETER XrmClient
    Xrm connector initialized to target instance. Use latest one by default. (CrmServiceClient)

    .PARAMETER Columns
    Specify expected columns to retrieve. (Default : all columns)
#>

function Get-XrmRootBusinessUnit {
    [CmdletBinding()]
    param
    ( 
        [Parameter(Mandatory = $false, ValueFromPipeline)]
        [Microsoft.Xrm.Tooling.Connector.CrmServiceClient]
        $XrmClient = $Global:XrmClient,        

        [Parameter(Mandatory = $false)]
        [ValidateNotNullOrEmpty()]
        [String[]]
        $Columns = @("*")
    )
    begin {
        $StopWatch = [System.Diagnostics.Stopwatch]::StartNew();
        Trace-XrmFunction -Name $MyInvocation.MyCommand.Name -Stage Start -Parameters ($MyInvocation.MyCommand.Parameters);       
    }    
    process {
        $queryBusinessUnit = New-XrmQueryExpression -LogicalName "businessunit" -Columns $Columns;
        $queryBusinessUnit = $queryBusinessUnit | Add-XrmQueryCondition -Field "parentbusinessunitid" -Condition Null;
        $businessUnits = $XrmClient | Get-XrmMultipleRecords -Query $queryBusinessUnit;
        $businessUnit = $businessUnits | Select-Object -First 1;
        $businessUnit;
    }
    end {
        $StopWatch.Stop();
        Trace-XrmFunction -Name $MyInvocation.MyCommand.Name -Stage Stop -StopWatch $StopWatch;
    }    
}
Export-ModuleMember -Function Get-XrmRootBusinessUnit -Alias *;