Function append

packages/react-stately/src/data/useTreeData.ts:338–349

(parentKey: Key | null, ...values: T[])

      this.insert(parentKey, 0, ...values);
    },
    append(parentKey: Key | null, ...values: T[]) {
      if (parentKey == null) {
        this.insert(null, items.length, ...values);
      } else {
        let parentNode = nodeMap.get(parentKey);
        if (!parentNode) {
          return;
        }

        this.insert(parentKey, parentNode.children!.length, ...values);
      }
    },
    remove(...keys: Key[]) {
      if (keys.length === 0) {
        return;