TreeRoot<T> class

A special tree node that serves as an invisible root container.

TreeRoot represents the invisible root of a tree structure that contains other tree nodes but doesn't appear in the visual tree. It's always considered expanded and never selected, serving purely as a container for organizing multiple top-level tree items.

This is useful when you need to group multiple tree items under a common parent without showing that parent in the tree view. All children of a TreeRoot appear at the top level of the tree.

TreeRoot maintains immutability like other tree nodes, but state update operations (expanded/selected) have no effect since these properties are fixed by design.

Example:

TreeRoot<String> root = TreeRoot(
  children: [
    TreeItem(data: 'First Section'),
    TreeItem(data: 'Second Section'),
    TreeItem(data: 'Third Section'),
  ],
);

// Root is always expanded and never selected
print(root.expanded); // true
print(root.selected); // false