Setting a crystal cluster

I purchased a cluster of amethyst with the thought that I would set
it in a bezel.

The problem I find is that the bottom of the base is smaller than
the top with the crystals - otherwide tapered.

It is oval shaped, approx. 23mm x 20mm. I am not sure how to make a
tapered bezel that size.

Would appreciate any suggestions.

I suppose I could set it using tabs/prongs, but you would be able to
see the sides which are a white/gray in color. My preference would be
that they not show.