Date tree ca be filed under entry. And reveal after jump.

doc/org.texi

@@ -5813,10 +5813,12 @@ to @code{org-remember-default-headline}.  If the file name is not an absolute
 path, it will be interpreted relative to @code{org-directory}.
 
 The heading can also be the symbols @code{top} or @code{bottom} to send notes
-as level 1 entries to the beginning or end of the file, respectively.  I may
-also be the symbol @code{date-tree}.  Then, a tree with year on level 1, month
-on level 2 and day on level three will be build in the file, and the entry
-will be filed into the tree under the current date.
+as level 1 entries to the beginning or end of the file, respectively.  It may
+also be the symbol @code{date-tree}.  Then, a tree with year on level 1,
+month on level 2 and day on level three will be build in the file, and the
+entry will be filed into the tree under the current date@footnote{If the file
+contains an entry with a @code{DATE_TREE} property, the entire date tree will
+be build under that entry.}
 
 An optional sixth element specifies the contexts in which the user can select
 the template.  This element can be a list of major modes or a function.
@@ -7635,20 +7637,22 @@ date at the cursor.
 @item i
 @vindex org-agenda-diary-file
 Insert a new entry into the diary, using the date at the cursor and (for
-clock entries) the date at the mark.  This will add to the Emacs diary
+block entries) the date at the mark.  This will add to the Emacs diary
 file@footnote{This file is parsed for the agenda when
 @code{org-agenda-include-diary} is set.}, in a way similar to the @kbd{i}
 command in the calendar.  The diary file will pop up in another window, where
 you can add the entry.
 
-If you configure @code{org-agenda-diary-file} to point to an Org-mode file
-instead, Org will create entries in that file.  Most entries will be stored
-in a date-based outline tree that will later make it easy to archive
-appointments from previous months/years.  Emacs will prompt you for the entry
-text - if you specify it, the entry will be created in
-@code{org-agenda-diary-file} without further interaction.  If you directly
-press @key{RET} at the prompt without typing text, the target file will be
-shown in another window for you to finish the entry there.
+If you configure @code{org-agenda-diary-file} to point to an Org-mode file,
+Org will create entries (in org-mode syntax) in that file instead.  Most
+entries will be stored in a date-based outline tree that will later make it
+easy to archive appointments from previous months/years.  The tree will be
+build under an entry with a @code{DATE_TREE} property, or else with years as
+top-level entries.  Emacs will prompt you for the entry text - if you specify
+it, the entry will be created in @code{org-agenda-diary-file} without further
+interaction.  If you directly press @key{RET} at the prompt without typing
+text, the target file will be shown in another window for you to finish the
+entry there.  See also the @kbd{k r} command.
 @c
 @kindex M
 @item M

lisp/org-agenda.el

@@ -6675,7 +6675,8 @@ The cursor may be at a date in the calendar, or in the Org agenda."
      ((equal char ?j)
       (org-switch-to-buffer-other-window
        (find-file-noselect org-agenda-diary-file))
-      (org-datetree-find-date-create d1))
+      (org-datetree-find-date-create d1)
+      (org-reveal t))
      (t (error "Invalid selection character `%c'" char)))))
 
 (defun org-agenda-add-entry-to-org-agenda-diary-file (type text &optional d1 d2)

lisp/org-datetree.el

@@ -33,11 +33,26 @@
 
 (require 'org)
 
+(defvar org-datetree-base-level 1
+  "The level at which years should be placed in the date tree.
+This is normally one, but if the buffer has an entry with a DATE_TREE
+property, the date tree will become a subtree under that entry, so the
+base level will be properly adjusted.")
+
 (defun org-datetree-find-date-create (date)
   "Find or create an entry for DATE."
   (let ((year (nth 2 date))
 	(month (car date))
 	(day (nth 1 date)))
+    (org-set-local 'org-datetree-base-level 1)
+    (widen)
+    (goto-char (point-min))
+    (when (re-search-forward "^[ \t]*:DATE_TREE:[ \t]+\\S-" nil t)
+      (org-back-to-heading t)
+      (org-set-local 'org-datetree-base-level
+		     (org-get-valid-level (funcall outline-level) 1))
+      (org-narrow-to-subtree))
+    (goto-char (point-min))
     (org-datetree-find-year-create year)
     (org-datetree-find-month-create year month)
     (org-datetree-find-day-create year month day)
@@ -103,7 +118,7 @@
   (let ((pos (point)))
     (skip-chars-backward " \t\n")
     (delete-region (point) pos)
-    (insert "\n* \n")
+    (insert "\n" (make-string org-datetree-base-level ?*) " \n")
     (backward-char 1)
     (if month (org-do-demote))
     (if day (org-do-demote))