Susan, it is an Adenium. I had bought it many many years ago as a very small plant, thinking I had Adenium obesum, but it simply took off, very unlike Adenium obesum. I lop off the top of the branches every few years or so.
The growth habit ( trunk) and size are typical for Adenium somalense, but looking at the flowers I suspect is a somalense hybrid, perhaps x with obesum. It blooms nicely every few months.
Here are some pictures from last year, but right now the plant is a lot greener.