diff --git a/.github/workflows/gh-pages.yaml b/.github/workflows/gh-pages.yaml
index e3e47963..8351e33c 100644
--- a/.github/workflows/gh-pages.yaml
+++ b/.github/workflows/gh-pages.yaml
@@ -17,7 +17,7 @@ jobs:
 
       - name: Install apt packages
         run: |
-          sudo apt-get install -y graphviz
+          sudo apt-get install -y graphviz tree
 
       - name: Set up Python
         uses: actions/setup-python@v4
diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index 70b76ed9..06a0000c 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -9,6 +9,7 @@ build:
     nodejs: "16"
   apt_packages:
     - graphviz
+    - tree
 
 sphinx:
   configuration: src/conf.py