diff --git a/runparams.py b/runparams.py
index 6b9951c..fd17feb 100644
--- a/runparams.py
+++ b/runparams.py
@@ -92,9 +92,9 @@ def check_input_path(p):
         desc_list = ["JSON dump", "MkDocs", "PlantUML", "RDF", "TeX", "Web pages"]
 
         if opts.verbose:
-            self.log.basicConfig(level=logging.INFO)
+            logging.basicConfig(level=logging.INFO)
         if opts.debug:
-            self.log.basicConfig(level=logging.DEBUG)
+            logging.basicConfig(level=logging.DEBUG)
 
         self.input_path = Path(opts.input_dir)
         check_input_path(self.input_path)
diff --git a/spec_parser/mkdocs.py b/spec_parser/mkdocs.py
index c7c2516..1a6174d 100644
--- a/spec_parser/mkdocs.py
+++ b/spec_parser/mkdocs.py
@@ -16,8 +16,12 @@ def gen_mkdocs(model, outpath, cfg):
     jinja.globals["class_link"] = class_link
     jinja.globals["property_link"] = property_link
     jinja.globals["ext_property_link"] = ext_property_link
-    jinja.globals["type_link"] = lambda x, showshort=False: type_link(x, model, showshort=showshort)
+    jinja.globals["type_link"] = lambda x, showshort=False: type_link(
+        x, model, showshort=showshort
+    )
     jinja.globals["not_none"] = lambda x: str(x) if x is not None else ""
+    jinja.globals["get_subclass_tree"] = lambda x: get_subclass_tree(x, model)
+    jinja.globals["get_class_url"] = get_class_url
 
     p = outpath
 
@@ -37,8 +41,23 @@ def _generate_in_dir(dirname, group, tmplfname):
             d.mkdir(exist_ok=True)
             f = d / f"{s.name}.md"
 
+            context = vars(s).copy()
+
+            # For classes, compute direct and nested subclasses
+            if dirname == "Classes" and hasattr(s, "subclasses"):
+                # Calculate direct subclasses (they are already stored in s.subclasses)
+
+                # Create a map of class to its direct subclasses (as Class objects, not just names)
+                direct_subclasses = []
+                for subclass_name in s.subclasses:
+                    subclass = model.classes.get(subclass_name)
+                    if subclass:
+                        direct_subclasses.append(subclass)
+
+                context["direct_subclasses"] = direct_subclasses
+
             template = jinja.get_template(tmplfname)
-            page = template.render(vars(s))
+            page = template.render(context)
             f.write_text(page)
 
     _generate_in_dir("Classes", model.classes, "class.md.j2")
@@ -52,7 +71,10 @@ def _gen_filelist(nsname, itemslist, heading):
         nameslist = [c.name for c in itemslist.values()]
         if nameslist:
             ret.append(f"    - {heading}:")
-            ret.extend(f"      - '{n}': model/{nsname}/{heading}/{n}.md" for n in sorted(nameslist))
+            ret.extend(
+                f"      - '{n}': model/{nsname}/{heading}/{n}.md"
+                for n in sorted(nameslist)
+            )
         return ret
 
     files = dict()
@@ -136,3 +158,42 @@ def type_link(name, model, *, showshort=False):
         return f"[{name}](../{dirname}/{name}.md)"
     else:
         return f"{name}"
+
+
+def get_subclass_tree(class_name, model):
+    """Build a nested structure representing the subclass tree for a given class.
+
+    Returns a list of dictionaries, each with 'name' and 'children' keys.
+    """
+    result = []
+    cls = model.classes.get(class_name)
+
+    if not cls or not hasattr(cls, "subclasses") or not cls.subclasses:
+        return result
+
+    for subclass_name in cls.subclasses:
+        subclass_info = {
+            "name": subclass_name,
+            "children": get_subclass_tree(subclass_name, model),
+        }
+        result.append(subclass_info)
+
+    return result
+
+
+def get_class_url(class_name):
+    """Generate a URL for a class based on its fully qualified name.
+
+    Args:
+        class_name: Fully qualified class name like "/Namespace/ClassName"
+
+    Returns:
+        URL string that works in MkDocs
+    """
+    parts = class_name.split("/")
+    if len(parts) >= 3:
+        namespace = parts[1]
+        class_name = parts[2]
+        # Format for MkDocs
+        return f"../../{namespace}/Classes/{class_name}"
+    return "#"
diff --git a/spec_parser/model.py b/spec_parser/model.py
index 43436e4..0003fe3 100644
--- a/spec_parser/model.py
+++ b/spec_parser/model.py
@@ -130,6 +130,20 @@ def _tsort_recursive(inh, cn, visited, stack):
                 c.inheritance_stack.append(pcn)
                 pcn = self.classes[pcn].fqsupercname
 
+        # build subclass trees
+        # Initialize subclasses dict for each class
+        for c in self.classes.values():
+            c.subclasses = []
+
+        # Populate subclasses
+        for c in self.classes.values():
+            if c.fqsupercname:
+                self.classes[c.fqsupercname].subclasses.append(c.fqname)
+
+        # Sort subclasses by name for consistent display
+        for c in self.classes.values():
+            c.subclasses.sort()
+
         # add inherited properties to classes
         for cn in stack:
             c = self.classes[cn]
diff --git a/spec_parser/templates/mkdocs/class.md.j2 b/spec_parser/templates/mkdocs/class.md.j2
index f47c063..c8274a9 100644
--- a/spec_parser/templates/mkdocs/class.md.j2
+++ b/spec_parser/templates/mkdocs/class.md.j2
@@ -22,6 +22,159 @@
   {% endif %}
 {% endfor %}
 
+{% if subclasses %}
+## Subclass tree
+
+{% set current_ns = fqname.split('/')[1] %}
+{% set current_name = fqname.split('/')[2] %}
+
+<ul class="tree-view">
+  <li>
+    <span class="tree-caret tree-caret-down"></span>
+    <span class="tree-text current-class">/{{current_ns}}/{{current_name}}</span>
+    {% set subclass_tree = get_subclass_tree(fqname) %}
+    {% if subclass_tree %}
+    <ul class="nested active">
+      {% macro render_tree_node(node) %}
+      <li>
+        {% set node_ns = node.name.split('/')[1] %}
+        {% set node_name = node.name.split('/')[2] %}
+        {% if node.children %}
+        <span class="tree-caret"></span>
+        <a href="/spdx-spec/model/{{node_ns}}/Classes/{{node_name}}" class="tree-text">/{{node_ns}}/{{node_name}}</a>
+        <ul class="nested">
+          {% for child in node.children %}
+          {{ render_tree_node(child) }}
+          {% endfor %}
+        </ul>
+        {% else %}
+        <span class="tree-leaf"></span>
+        <a href="/spdx-spec/model/{{node_ns}}/Classes/{{node_name}}" class="tree-text">/{{node_ns}}/{{node_name}}</a>
+        {% endif %}
+      </li>
+      {% endmacro %}
+      
+      {% for node in subclass_tree %}
+      {{ render_tree_node(node) }}
+      {% endfor %}
+    </ul>
+    {% endif %}
+  </li>
+</ul>
+
+<style>
+/* Tree View Styles */
+.tree-view, .tree-view ul, .tree-view li {
+  list-style: none !important;
+  list-style-type: none !important;
+  list-style-image: none !important;
+  margin: 0;
+  padding: 0;
+}
+
+.tree-view {
+  padding-left: 0;
+  font-family: inherit;
+}
+
+.tree-view ul {
+  padding-left: 20px;
+  margin: 5px 0;
+}
+
+.tree-view li {
+  margin: 5px 0;
+  position: relative;
+}
+
+/* Override any markdown list styles */
+.tree-view li::before,
+.tree-view li::marker,
+.tree-view li::after {
+  content: none !important;
+  display: none !important;
+}
+
+.tree-caret,
+.tree-leaf {
+  display: inline-block;
+  width: 16px;
+  height: 16px;
+  text-align: center;
+  vertical-align: middle;
+}
+
+.tree-caret {
+  cursor: pointer;
+  user-select: none;
+}
+
+.tree-caret::before {
+  content: "▶";
+  color: #555;
+  display: inline-block;
+  transition: transform 0.2s;
+  font-size: 0.8em;
+}
+
+.tree-caret-down::before {
+  transform: rotate(90deg);
+}
+
+.tree-text {
+  vertical-align: middle;
+}
+
+.current-class {
+  font-weight: bold;
+}
+
+.nested {
+  display: none;
+}
+
+.active {
+  display: block;
+}
+
+/* Fix MkDocs link styles in tree */
+.tree-view a {
+  color: inherit;
+  text-decoration: none;
+}
+
+.tree-view a:hover {
+  text-decoration: underline;
+}
+</style>
+
+<script>
+// Tree view behavior - optimized
+(function() {
+  function initTreeView() {
+    document.querySelectorAll('.tree-caret').forEach(function(toggler) {
+      toggler.addEventListener('click', function(e) {
+        e.preventDefault();
+        e.stopPropagation();
+        this.classList.toggle('tree-caret-down');
+        this.parentElement.querySelector('.nested').classList.toggle('active');
+      });
+    });
+  }
+
+  // Run when DOM is ready
+  if (document.readyState !== 'loading') {
+    initTreeView();
+  } else {
+    document.addEventListener('DOMContentLoaded', initTreeView);
+  }
+
+  // Also run when MkDocs finishes loading
+  document.addEventListener('DOMContentSwapComplete', initTreeView);
+})();
+</script>
+{% endif %}
+
 {% endblock %}
 
 {% block extra %}