[discussion] Add Tree Select component?

*⚠️ Info: This issue is for product research, to gather community input. In this [base-ui repo](https://github.com/mui/base-ui) we are, currently, focused on the core set of components needed to create a great design system, so the probability we build this in this repo is very low.*

## Summary

## Examples in other libraries

- https://ant.design/components/tree-select/
- https://github.com/react-component/tree-select
- https://www.telerik.com/kendo-react-ui/components/dropdowns/multiselecttree/
- https://primereact.org/treeselect/
- https://www.syncfusion.com/react-components/react-dropdown-tree

*([internal benchmark](https://www.notion.so/mui-org/x-Tree-Select-component-35ccbfe7b660801e8270fb8d191b8327))*

## Motivation

TBD

- User requests:
- https://x.com/_thomasholland/status/2041459749162525124
- UI library requests:
- https://github.com/shadcn-ui/ui/issues/1875
- https://github.com/mui/mui-x/issues/514