Custom alerts for different WhatsApp groups"

I've given into pressure and installed WhatsApp and want to have a different meaningful (thus customised) "alert tones" for different groups.

I've figured out how to edit groups but when I choose "wallpaper & sound>Alert tone", in WhatsApp, I just get a short list of Apple "alert tones" which is not even the full list of available Apple sounds for text message alerts.

Now, like many, I have crafted some instantly recognisable "alert tones" for text messaging but cannot seem to be able to get to then from WhatsApp.

What's occurring?