create a new dir for nerdtree plugins

plugin/NERD_tree.vim

@@ -158,6 +158,9 @@ augroup NERDTree
     exec "autocmd BufWinLeave *". s:NERDTreeBufName ." call <SID>saveScreenState()"
     "cache bookmarks when vim loads
     autocmd VimEnter * call s:Bookmark.CacheBookmarks(0)
+
+    "load all nerdtree plugins after vim starts
+    autocmd VimEnter * runtime! nerdtree_plugin/*.vim
 augroup END
 
 if g:NERDTreeHijackNetrw