Need help to implement "+" animation for nested nodes

[sathya-1994]

I am using GLSP's vscode extension(https://github.com/eclipse-glsp/glsp-vscode-integration) and language server which extends GLSP server.

I am creating nodes using GModel.
Screenshot:

I want to add + button to display/hide nested nodes. How we can implement this feature?
Or Already this implementation is available in GLSP?
Screenshot:

My idea: When user click "+" icon, we will call layout operation and we will add/remove child/nested nodes while layout generation based on the boolean value(new filed added to model state) stored in the model state(org.eclipse.glsp.server.model.GModelState). We will update this new filed when user clicks "+" icon.

Graph hierarchy:

[planger]

There are a few different approaches to implement such a button feature:

• Add a placeholder node (GModelElement, such as a label etc) to the GModel and register a client-side click listener, which sends whatever action you need on click
• Register a client-side UIExtension (HTML) that is rendered on top of the diagram on each element, which will again on click send whatever action you need
• Use GButton, which is a GModelElement. I haven't used this for quite some time though.