diff --git a/examples/ui.rs b/examples/ui.rs
index 7412578..a62faa6 100644
--- a/examples/ui.rs
+++ b/examples/ui.rs
@@ -5,13 +5,12 @@ use games::*;
 fn main() {
     let mut app = App::new();
     app.add_plugins(BaseGamePlugin::default())
-        .add_systems(Startup, setup);
+        .add_systems(Startup, (setup_list, setup_nav_tree))
+        .add_systems(Update, run_tree.run_if(any_component_changed::<NavTree>));
     app.run();
 }
 
-const LINE_HEIGHT: f32 = 21.;
-
-fn setup(mut commands: Commands) {
+fn setup_list(mut commands: Commands) {
     // Scrolling list
     commands
         .spawn((
@@ -23,7 +22,7 @@ fn setup(mut commands: Commands) {
                 overflow: Overflow::scroll(),
                 ..default()
             },
-            BackgroundColor(Color::srgb(0.10, 0.10, 0.10)),
+            BackgroundColor(RED.into()),
         ))
         .with_children(|parent| {
             // List items
@@ -34,20 +33,69 @@ fn setup(mut commands: Commands) {
         .observe(scroll);
 }
 
-/// Updates the scroll position of scrollable nodes in response to mouse input
-pub fn scroll(
-    trigger: Trigger<Pointer<Scroll>>,
-    mut scrollers: Query<&mut ScrollPosition>,
-) {
-    let Pointer { event: Scroll { unit, x, y, .. }, .. } = trigger.event();
-
-    let (dx, dy) = match unit {
-        MouseScrollUnit::Line => (x * LINE_HEIGHT, y * LINE_HEIGHT),
-        MouseScrollUnit::Pixel => (x * 1., y * 1.),
-    };
+fn setup_nav_tree(mut commands: Commands) {
+    // Nav Tree
+    commands
+        .spawn((
+            Node {
+                position_type: PositionType::Absolute,
+                right: Val::Px(0.0),
+                width: Val::Px(100.0),
+                height: Val::Px(100.0),
+                ..default()
+            },
+            BackgroundColor(RED.into()),
+            NavTree::Closed,
+        ))
+        .with_children(|parent| {
+            parent
+                .spawn((
+                    Node {
+                        position_type: PositionType::Absolute,
+                        right: Val::Px(100.0),
+                        width: Val::Px(100.0),
+                        height: Val::Px(100.0),
+                        ..default()
+                    },
+                    BackgroundColor(ORANGE.into()),
+                    NavTree::Closed,
+                ))
+                .with_children(|parent| {
+                    parent.spawn((
+                        Node {
+                            position_type: PositionType::Absolute,
+                            right: Val::Px(100.0),
+                            width: Val::Px(100.0),
+                            height: Val::Px(100.0),
+                            ..default()
+                        },
+                        BackgroundColor(YELLOW.into()),
+                        NavTree::Closed,
+                    ));
+                });
+        });
+}
 
-    if let Ok(mut pos) = scrollers.get_mut(trigger.target()) {
-        pos.offset_x -= dx;
-        pos.offset_y -= dy;
-    }
+fn run_tree(
+    q: Query<(Entity, &NavTree), Changed<NavTree>>,
+    children: Query<&Children>,
+    mut query: Query<(&ChildOf, &mut Visibility)>,
+) {
+    q.iter().for_each(|(e, nav)| {
+        // todo!("Clean this code up please!");
+        match nav {
+            NavTree::Open => children.iter_descendants(e).for_each(|child| {
+                let (co, mut v) = query.get_mut(child).unwrap();
+                if ChildOf(e) == *co {
+                    *v = Visibility::Inherited;
+                }
+            }),
+            NavTree::Closed => children.iter_descendants(e).for_each(|child| {
+                let (co, mut v) = query.get_mut(child).unwrap();
+                if ChildOf(e) == *co {
+                    *v = Visibility::Hidden;
+                }
+            }),
+        }
+    });
 }
diff --git a/src/ui.rs b/src/ui.rs
index 0049660..7f20d8e 100644
--- a/src/ui.rs
+++ b/src/ui.rs
@@ -4,7 +4,10 @@ pub(crate) struct BaseUiPlugin;
 
 impl Plugin for BaseUiPlugin {
     fn build(&self, app: &mut App) {
-        // Nope!
+        app.add_systems(
+            Update,
+            nav_tree.run_if(on_event::<Pointer<Over>>.or(on_event::<Pointer<Out>>)),
+        );
     }
 }
 
@@ -23,3 +26,88 @@ pub fn sync_resource_to_ui<R: Resource + Default + Display>(
         t.0 = format!("{}", *r);
     });
 }
+
+/// Updates the scroll position of scrollable nodes in response to mouse input
+pub fn scroll(trigger: Trigger<Pointer<Scroll>>, mut scrollers: Query<&mut ScrollPosition>) {
+    let Pointer {
+        event: Scroll { unit, x, y, .. },
+        ..
+    } = trigger.event();
+
+    let (dx, dy) = match unit {
+        MouseScrollUnit::Line => (x * 16.0, y * 16.0),
+        MouseScrollUnit::Pixel => (x * 1., y * 1.),
+    };
+
+    if let Ok(mut pos) = scrollers.get_mut(trigger.target()) {
+        pos.offset_x -= dx;
+        pos.offset_y -= dy;
+    }
+}
+
+#[derive(Component, Debug)]
+pub enum NavTree {
+    Open,
+    Closed,
+}
+
+impl NavTree {
+    fn open(&mut self) {
+        *self = NavTree::Open;
+    }
+
+    fn close(&mut self) {
+        *self = NavTree::Closed;
+    }
+}
+
+pub fn nav_tree(
+    mut over: EventReader<Pointer<Over>>,
+    mut out: EventReader<Pointer<Out>>,
+    mut query: Query<&mut NavTree>,
+    parents: Query<&Children>,
+    children: Query<&ChildOf>,
+) {
+    // Get the entity that was just moused over (if any)
+    // Open this nav tree
+    let opens: Vec<Entity> = over
+        .read()
+        .filter_map(|over| {
+            query
+                .get_mut(over.target)
+                .map(|mut n| {
+                    n.open();
+                    over.target
+                })
+                .ok()
+        })
+        .collect();
+
+    // Close this nav tree if it is moused off
+    //   and none of it's descendants were moused over
+    out.read().for_each(|out| {
+        if let Ok(mut nav) = query.get_mut(out.target) {
+            // Check if any of the opened entities is a child of this UI element
+            let mouse_over_child = parents
+                .iter_descendants(out.target)
+                .any(|child| opens.contains(&child));
+            if !mouse_over_child {
+                // Mouse still on nav tree
+                nav.close();
+
+                // Check if the mouse is over any ancestors
+                let mouse_over_parent = children
+                    .iter_ancestors(out.target)
+                    .any(|parent| opens.contains(&parent));
+                if !mouse_over_parent {
+                    info!("Mouse is not over this tree");
+                    children.iter_ancestors(out.target).for_each(|e| {
+                        query.get_mut(e).iter_mut().for_each(|nav| {
+                            nav.close();
+                        });
+                    });
+                }
+            }
+        }
+    });
+}