need help to implement multilevel inner circle

[AnanthGopal]

Hi,

https://observablehq.com/@dianaow/force-directed-graph-with-circle-packing/2
you are doing great work on d3 force-directed-graph-with-circle-packing, I try to add multiple inner circles into d3 but I can't achieve it.

For Example
Draw the two inner circles into the root node like

we try to add two or more circle into child circle like below