Tree widget: Parent/child elements visibility controls in Models tree are inconsistent

[grigasp]

1. Open http://localhost:3000/?iTwinId=b391ba44-add7-47a0-8375-f2889a3540e8&iModelId=ba504f88-a479-4156-9d81-658ee169588e in test viewer
2. Expand "ProcessPhysicalModel" model, "E-HEX" category, "Plate-type Heat Exchanger" elements' class grouping node, "E-102 [4-1MG]" element. The "E-102 [4-1MG]" element has its own geometry, but it also has geometric Nozzle child elements.
3. Changing visibility of Nozzle child elements doesn't affect visibility of the parent "E-102 [4-1MG]" element.
4. Changing visibility of "E-102 [4-1MG]" parent element doesn't affect visibility of its children.

How should it work, keeping in mind that parent has its own geometry? The first solution that comes to mind is that when a parent is turned off, its children should also be turned off. But what if a user wants to only turn off the parent, but not the children?