Function insert

packages/react-stately/src/data/useTreeData.ts:284–313

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

      return nodeMap.get(key);
    },
    insert(parentKey: Key | null, index: number, ...values: T[]) {
      setItems(({items, nodeMap: originalMap}) => {
        let {items: newNodes, nodeMap: newMap} = buildTree(values, new Map(originalMap), parentKey);

        // If parentKey is null, insert into the root.
        if (parentKey == null) {
          return {
            items: [...items.slice(0, index), ...newNodes, ...items.slice(index)],
            nodeMap: newMap
          };
        }

        // Otherwise, update the parent node and its ancestors.
        return updateTree(
          items,
          parentKey,
          parentNode => ({
            key: parentNode.key,
            parentKey: parentNode.parentKey,
            value: parentNode.value,
            children: [
              ...parentNode.children!.slice(0, index),
              ...newNodes,
              ...parentNode.children!.slice(index)
            ]
          }),
          newMap
        );
      });
    },
    insertBefore(key: Key, ...values: T[]): void {
      let node = nodeMap.get(key);
      if (!node) {