best way to display a "window" below of StatusIcon

[Victor Aurélio Santos <victoraur santos gmail com>]

What's the best way to display a "window" below of a StatusIcon
like Mixers do ?

I'm writing a Mixer using in GTK-3 and need to display some Scales and
Labels bellow (or above depending where Notification are resides)
StatusIcon, what's best way do this ? I've searched but found nothing...

An example can be helpful, I'm developing in GTKmm but an example any
other (C, Python,...) can help me

Thanks in Advance