Hi Thierry,
Sorry, I see that you were clear from the start about Cluster Variables platform, but I just wasn't reading properly. I found 2 ways to make an almost dendrogram, perhaps others in the community can improve these or provide better ideas. I started by making the Cluster Members table into a data table. The first method was a Diagram:
To force this into just one diagram instead of a separate one for each cluster, I added a '0' cluster to the bottom of the data table:
I also made something in Graph Builder:
To get this, I had to add a 'Main' column to the data table, and I had to create a manual Value Ordering sort order for the Members column.
I attached a data table, and I'm hoping others might have better ideas (perhaps graphing guru @scwise).
Thanks for helping me see what you're looking for.
Jed