you want to tag a whole thread in `notmuch-tree-mode` use
`notmuch-tree-tag-thread` instead of `notmuch-tree-tag`.
+You may also want the function in search mode apply to the all threads
+in the selected region (if there is one). For notmuch prior to 0.17
+this behaviour will occur automatically with the functions given
+above. To get this behaviour on 0.17+ do the following:
+
+ (define-key notmuch-search-mode-map "S"
+ (lambda (&optional beg end)
+ "mark thread as spam"
+ (interactive (notmuch-search-interactive-region))
+ (notmuch-search-tag (list "+spam" "-inbox") beg end)))
+
+The analogous functionality in notmuch-tree is currently missing.
+
The definitions above make use of a lambda function, but you could
also define a separate function first: