How to make rows expandable/retractable with subTable?

Question

I'm actually working in a project where i'm using Java Primefaces and I need to create a datatable that group elements under multiple categories The render.

I want to be able to retract the category and only have the title of the category and make the items of that category hidden.

My datatable looks like this actually :

<p:dataTable id="datatable-assistant" value="#{resultatFiscalAvanceHandler.subTable}" var="_regroupement" editable="true" editMode="cell" rowIndexVar="index">
<p:subTable value="#{_regroupement.paramsAssistantAvance}" var="_param">
//The columns
</p:subTable>
</p:dataTable>

I tried using the rowGroup feature from PrimeFaces (https://www.primefaces.org/showcase/ui/data/datatable/rowGroup.xhtml?jfwid=6cac1) but I've got stuck in how I could nest it. (I could create the categories and show the titles of them, but I couldn't wrap my head around how to list the elements inside them)