Since Bookmarks are displayed on top of the tree, you can create a Bookmark of you working dir. Move to the working dir and type :Bookmark
in command mode. The name of the dir appears in curly braces next to the dir name. (Be aware that no spaces are in dir name. Is that the case, you have to name the Bookmark by you own with Bookmark <name>
).
To display Bookmarks, type B
in NERDTree buffer.
Have also a look into the help: :help nerdtree