Create universal fern tree

autoload/fern.vim

@@ -36,6 +36,7 @@ call s:Config.config(expand('<sfile>:p'), {
       \ 'disable_drawer_auto_resize': 0,
       \ 'disable_drawer_smart_quit': get(g:, 'disable_drawer_auto_quit', 0),
       \ 'disable_drawer_hover_popup': 0,
+      \ 'disable_drawer_tabpage_isolation': 0,
       \ 'disable_drawer_auto_restore_focus': 0,
       \ 'default_hidden': 0,
       \ 'default_include': '',

autoload/fern/internal/command/fern.vim

@@ -71,6 +71,9 @@ function! fern#internal#command#fern#command(mods, fargs) abort
           \   ? printf('drawer-right:%d', tabpagenr())
           \   : printf('drawer:%d', tabpagenr())
           \ : ''
+    if drawer && g:fern#disable_drawer_tabpage_isolation
+      let fri.authority = right ? 'drawer-right:0' : 'drawer:0'
+    endif
     let fri.query = extend(fri.query, {
           \ 'width': width,
           \ 'keep': keep,

autoload/fern/internal/viewer/auto_duplication.vim

@@ -1,5 +1,6 @@
 function! fern#internal#viewer#auto_duplication#init() abort
-  if g:fern#disable_viewer_auto_duplication
+  if g:fern#disable_viewer_auto_duplication ||
+    \ (g:fern#disable_drawer_tabpage_isolation && fern#internal#drawer#is_drawer())
     return
   endif
 

doc/fern.txt

@@ -421,6 +421,14 @@ VARIABLE						*fern-variable*
 
 	Default: 0
 
+*g:fern#disable_drawer_tabpage_isolation*
+	Set 1 to disable the drawer tabpage isolation.
+
+        If disabled, there is only one left or right drawer across the all the
+        windows and tabs for a given VIM instance.
+
+        Default: 0
+
 *g:fern#disable_drawer_smart_quit*
 	Set 1 to disable smart quit behavior when there are only two buffer
 	remains (one is for the drawer styled fern window.)