I've removed its working directory, because this git working tree is no longer useful, then I git branch -D pubsub-sketch-tree at the directory of main repository. An error thrown:
error: Cannot delete branch 'pubsub-sketch-tree' checked out at '/Users/zhouhancheng/编程/github_own/sketch_worktree/pubsub-sketch_tree'
But '/Users/zhouhancheng/编程/github_own/sketch_worktree/pubsub-sketch_tree' had been removed.