Add the "collapse" and "open" functions to TreeView in python

[santelelle]

Checklist

• I have searched for similar issues.
• For Python issues, I have tested with the latest development wheel.
• I have checked the release documentation and the latest documentation (for main branch).

Proposed new feature or change

When adding many items to the TreeView (with different hierarchies) the widget get crowded very quickly. It's possible to collapse and open a single parent item from the interface with the mouse, but I could not find a way to do it from code.

I would like to have the option to collapse and open them via code.

References

No response

Additional information

No response

[MiriShulman]

Hi, thanks for raising this feature request.

I’d be happy to work on this if it aligns with the project’s direction.

My initial thought is to expose simple Python API methods, for example:

• tree.collapse(item_id)
• tree.expand(item_id)
  (or similar naming, if there is an existing convention)

This would allow programmatic control over TreeView hierarchy state, matching the existing mouse-based behavior.

Before starting implementation, I’d appreciate confirmation that this approach makes sense from a design/API perspective.
If so, I can prepare a PR.

Thanks!

[santelelle]

I've found a component that has a similar behaviour with the functions already existing: CollapsableVert. It might be better to keep the same naming convention get_is_open(item_id) and set_is_open(item_id).

get_is_open(self: [open3d.visualization.gui.CollapsableVert](https://www.open3d.org/docs/release/python_api/open3d.visualization.gui.CollapsableVert.html#open3d.visualization.gui.CollapsableVert)) → bool Check if widget is open.

set_is_open(self: open3d.visualization.gui.CollapsableVert, is_open: bool) → None Sets to collapsed (False) or open (True). Requires a call to Window.SetNeedsLayout() afterwards, unless calling before window is visible

https://www.open3d.org/docs/release/python_api/open3d.visualization.gui.CollapsableVert.html