diff --git a/tree/README.md b/tree/README.md
index 6cc7744..6aa92a1 100644
--- a/tree/README.md
+++ b/tree/README.md
@@ -8,3 +8,5 @@ This will make the output "pretty" (i.e. indented).
 To print the output to terminal, run `python tree.py`
 
 To save to a file, run `python tree.py file.html`.
+
+To append to an already existing file, run `python tree.py >> file.html`