Just as you can import references from external files into your scene, you can also export objects in your scene to external files and keep them as references.
 -click willow1MeshGroup and select Reference > Export Selection As Reference >
-click willow1MeshGroup and select Reference > Export Selection As Reference >  from the menu that appears.
 from the menu that appears. 
                
            If you check the Outliner, you can see a new reference node entry called treeRN. The main scene is now referencing the tree from an external file, just like your zombies.
 Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License
 Except where otherwise noted, this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License