Great design! Good re-use, showing the flexibility of facet as a base-component for other compositions.

A lot of my intuition on this is based on the absense of a left/down chevron, which the industry usually uses to show collapsed/shown accordion (and in fact is on Accordion). I am +1 on this absense, and I think the children-count indication is excellent and I feel is the thing that allows the exclusion of the chevron. Kind of traded-up the chevron for an equally appropriate indicator that gives more information.

Counter-intuitively, I would choose "selected" state for Collapsed tree segements. In my mind this would bring attention to things the user is not seeing. I feel like an expanded tree segment is highlight-enough in its own right.
I feel that color-changing the children-count is not desired. I think the color contrast would become a cognitive dischord, getting in the way of the understanding of the information itself - the tree and its content.

@anirudha

@pjfitzgibbons I may have caused some confusion by referencing facet styling here. OuiTreeView already exists and the expand / collapse icons can be set by the builder - they can be chevrons or other icons (like folders) : https://oui.opensearch.org/1.2/#/navigation/tree-view

Since count would be optional in OuiTreeNav, we would still want to use expand/collapse indicators. Builders may also choose to force expand the tree as well.

For clarity - this component doesn't contain facet - for the sake of speed/ not having to red-line a design or cause an inconsistency, I was pointing to the design of count on OuiFacet and OuiFilterGroup for the builder to reference.

Can you take a look at the OUI Docs for Tree view and see if the way icons for expand/collapse give you any concerns or questions ?

OK. looking. You references "OuiTreeNav".. are you considering adding a new/fork component here? I don't understand the difference vs OuiTreeView.
And I didn't realize OuiTreeView was pre-existing... will investigate.

@pjfitzgibbons No, not a fork or a new component, this is just an additional prop within the existing component. Right now there is no count in tree view today.

Here is what tree view looks like currently:

I can take this issue. Basically a count prop that is displayed next to the labels of the tree view that mirrors OuiFacet's count prop?