gnu: Add emacs-tree-mode.

* gnu/packages/emacs.scm (emacs-tree-mode): New public variable.

gnu/packages/emacs.scm

@@ -8426,3 +8426,27 @@ orient yourself in the code, and tell which statements are at a given level.")
     (description "This package provides an Emacs library to create, query,
 navigate and display hierarchy structures.")
     (license license:gpl3+)))
+
+(define-public emacs-tree-mode
+  (let ((commit "b06078826d5875d74b0e7b7ac47b0d0917610534")
+        (revision "1"))
+    (package
+      (name "emacs-tree-mode")
+      (version (string-append "0.0.1" "-" revision "."
+                              (string-take commit 7)))
+      (source
+       (origin
+         (method git-fetch)
+         (uri (git-reference
+               (url "https://github.com/emacsorphanage/tree-mode.git")
+               (commit commit)))
+         (file-name (string-append name "-" version "-checkout"))
+         (sha256
+          (base32
+           "13bbdhdmqg4x9yghanhr8fsbsxbnypzxdxgicz31sjjm675kpnix"))))
+      (build-system emacs-build-system)
+      (home-page "https://github.com/emacsorphanage/tree-mode")
+      (synopsis "Emacs mode to manage tree widgets")
+      (description
+       "This package provides an Emacs library to manage tree widgets.")
+      (license license:gpl3+))))