diff --git a/prepare-vms/lib/postprep.py b/prepare-vms/lib/postprep.py
index d5970d54..1c4ed4d9 100755
--- a/prepare-vms/lib/postprep.py
+++ b/prepare-vms/lib/postprep.py
@@ -108,7 +108,7 @@ system("sudo chmod +x /usr/local/bin/docker-machine")
 system("docker-machine version")
 
 system("sudo apt-get remove -y --purge dnsmasq-base")
-system("sudo apt-get -qy install python-setuptools pssh apache2-utils httping htop unzip mosh")
+system("sudo apt-get -qy install python-setuptools pssh apache2-utils httping htop unzip mosh tree")
 
 ### Wait for Docker to be up.
 ### (If we don't do this, Docker will not be responsive during the next step.)