Thanks Steve! This is a lot closer to what I was able to achieve. It looks good! I will use this. 
I thought that it is tricky to do it with the current abilities. I was therefore looking for guidance to do some coding. If I/anyone would want to extend the Graphviz code for a new type of node then what do I need to consider? is there any documentation on this?
I see that my question doesn’t fully show my intention.
Thanks for providing me this.