Build a semi-accessible file explorer in React that displays files and directories in a hierarchical tree format with appropriate ARIA roles and properties.

Requirements:

1. Display names of files and directories in a tree view.
2. Directories:
   • Can contain other directories and files.
   • Should be expandable/collapsible by clicking.
   • Should be displayed before files and sorted alphabetically.
   • Can be empty.
3. Files:
   • Are leaf nodes and cannot be expanded.
4. Indent contents to represent hierarchy visually.
5. Accessibility:
   • Use role="tree" for the container.
   • Use role="treeitem" for each node.
   • Directories should use aria-expanded to indicate state.
   • Nested content should have role="group".
   • Focus on correct roles/states, not keyboard navigation (semi-accessible).