Function buildTree

packages/react-stately/src/data/useTreeData.ts:166–189

(
    initialItems: T[] | null = [],
    map: Map<Key, TreeNode<T>>,
    parentKey?: Key | null
  )

  let [selectedKeys, setSelectedKeys] = useState(new Set<Key>(initialSelectedKeys || []));

  function buildTree(
    initialItems: T[] | null = [],
    map: Map<Key, TreeNode<T>>,
    parentKey?: Key | null
  ) {
    if (initialItems == null) {
      initialItems = [];
    }
    return {
      items: initialItems.map(item => {
        let node: TreeNode<T> = {
          key: getKey(item),
          parentKey: parentKey ?? null,
          value: item,
          children: null
        };

        node.children = buildTree(getChildren(item), map, node.key).items;
        map.set(node.key, node);
        return node;
      }),
      nodeMap: map
    };
  }

  function updateTree(
    items: TreeNode<T>[],