[Vue warn]: Unknown custom element: <TreeNode> - did you register the component correctly? For recursive components, make sure to provide the "name" option.

遞歸式引用組件，比如A組件引用B組件，B組件引用C組件，C組件又引用A組件之類的
解決方案是，將import引入改為components內引入：

components: {
  TreeNode: () => import('./TreeNode.vue')
}