diff --git a/crates/ui-egui/src/panels/timeline.rs b/crates/ui-egui/src/panels/timeline.rs
index 72f104290..afa656ac9 100644
--- a/crates/ui-egui/src/panels/timeline.rs
+++ b/crates/ui-egui/src/panels/timeline.rs
@@ -2177,7 +2177,8 @@ pub fn show(app: &mut EffectcraftApp, ui: &mut egui::Ui, rect: Rect) {
                 if *has_children {
                     let tw = Rect::from_center_size(pos2(indent, cy), vec2(13.0, 13.0));
                     if widgets::twirl(ui, tw, *open, egui::Id::new(("gtw", uid)), &t).clicked() {
-                        ui_actions.push(UiAct::ToggleGroup(*uid));
+                        // Alt/Cmd-click twirls the whole tree under the group (as on a layer).
+                        ui_actions.push(UiAct::ToggleGroup(layer.id.0, *uid, ui.input(|i| i.modifiers.alt || i.modifiers.command)));
                     }
                     app.auto.add(&format!("timeline.group.{uid}.twirl"), tw, name);
                 }
@@ -2246,7 +2247,7 @@ pub fn show(app: &mut EffectcraftApp, ui: &mut egui::Ui, rect: Rect) {
                         actions.push(("prop.select".into(), json!({"layer": layer.id.0, "prop": uid, "selectKeys": false})));
                         actions.push(("window.panel".into(), json!({"panel": "EffectControls"})));
                     } else {
-                        ui_actions.push(UiAct::ToggleGroup(*uid));
+                        ui_actions.push(UiAct::ToggleGroup(layer.id.0, *uid, false));
                     }
                 }
             }
@@ -3103,9 +3104,22 @@ pub fn show(app: &mut EffectcraftApp, ui: &mut egui::Ui, rect: Rect) {
                     }
                 }
             }
-            UiAct::ToggleGroup(uid) => {
-                if !app.ui.timeline.open_groups.remove(&uid) {
-                    app.ui.timeline.open_groups.insert(uid);
+            UiAct::ToggleGroup(layer, uid, all) => {
+                let tl = &mut app.ui.timeline;
+                let open = !tl.open_groups.remove(&uid);
+                if open {
+                    tl.open_groups.insert(uid);
+                }
+                if all && let Some(g) = comp.layer(LayerId(layer)).and_then(|l| find_group(&l.props, uid)) {
+                    let mut uids = vec![];
+                    walk_groups(g, &mut uids);
+                    for u in uids {
+                        if open {
+                            tl.open_groups.insert(u);
+                        } else {
+                            tl.open_groups.remove(&u);
+                        }
+                    }
                 }
             }
             UiAct::SetTime(tt) => app.session.set_time(tt),
@@ -3229,7 +3243,8 @@ fn layer_cells(
 
 enum UiAct {
     ToggleLayer(u64, bool),
-    ToggleGroup(u64),
+    /// Layer, group uid, and whether the whole tree under the group follows.
+    ToggleGroup(u64, u64, bool),
     SetTime(Tick),
     EndMerge,
     /// Composition Settings on its 3D Renderer tab.
@@ -3243,6 +3258,11 @@ fn walk_groups(g: &PropGroup, out: &mut Vec<u64>) {
     }
 }
 
+/// The group `uid` anywhere under `g`.
+fn find_group(g: &PropGroup, uid: u64) -> Option<&PropGroup> {
+    g.groups().find_map(|sg| if sg.uid == uid { Some(sg) } else { find_group(sg, uid) })
+}
+
 /// A stroke's Dashes "+" / "−" buttons (add or remove a Dash/Gap pair).
 #[allow(clippy::too_many_arguments)]
 fn dash_buttons(
diff --git a/crates/ui-egui/tests/ui_viewer.rs b/crates/ui-egui/tests/ui_viewer.rs
index 07036ca81..bfe4a3f67 100644
--- a/crates/ui-egui/tests/ui_viewer.rs
+++ b/crates/ui-egui/tests/ui_viewer.rs
@@ -1570,6 +1570,52 @@ fn timeline_twirl_arrows_open_layers_and_groups() {
     assert!(!shown(&h, prop_uid(&h, "Box", "transform/position")));
 }
 
+#[test]
+fn command_clicking_a_group_twirl_opens_its_whole_tree() {
+    // Cmd-click (or Alt-click) the arrow of Effects, Contents, Masks…: every group under it
+    // twirls open with it, and closed again with it.
+    let mut h = harness();
+    let id = layer_id(&h, "Box");
+    h.state_mut().session.execute("effect.apply", json!({"effect": "Lumetri Color", "layers": [id]})).unwrap();
+    fn walk(g: &effectcraft_engine::project::PropGroup, out: &mut Vec<u64>) {
+        for sg in g.groups() {
+            out.push(sg.uid);
+            walk(sg, out);
+        }
+    }
+    let (effects, inner, transform) = {
+        let comp = h.state().session.active_comp().unwrap().clone();
+        let props = &comp.layer(LayerId(id)).unwrap().props;
+        let fx = props.sub("effects").unwrap();
+        let mut inner = vec![];
+        walk(fx, &mut inner);
+        (fx.uid, inner, props.sub("transform").unwrap().uid)
+    };
+    assert!(inner.len() > 1, "the effect has twirl-down groups of its own");
+    let at = rect(&h, &format!("timeline.layer.{id}.twirl")).center();
+    click(&mut h, at);
+    let at = rect(&h, &format!("timeline.group.{effects}.twirl")).center();
+    let cmd_click = |h: &mut Harness<'_, EffectcraftApp>| {
+        h.input_mut().events.push(Event::ModifiersChanged(egui::Modifiers::COMMAND));
+        h.input_mut().events.push(Event::PointerMoved(at));
+        h.step();
+        for pressed in [true, false] {
+            h.input_mut().events.push(Event::PointerButton { pos: at, button: egui::PointerButton::Primary, pressed, modifiers: egui::Modifiers::COMMAND });
+            h.step();
+        }
+        h.input_mut().events.push(Event::ModifiersChanged(Default::default()));
+        h.step();
+    };
+    cmd_click(&mut h);
+    let open = h.state().ui.timeline.open_groups.clone();
+    assert!(open.contains(&effects), "Effects twirls open");
+    assert!(inner.iter().all(|u| open.contains(u)), "and so does everything under it");
+    assert!(!open.contains(&transform), "other groups stay as they were");
+    cmd_click(&mut h);
+    let open = h.state().ui.timeline.open_groups.clone();
+    assert!(!open.contains(&effects) && !inner.iter().any(|u| open.contains(u)), "Cmd-click again closes the tree");
+}
+
 #[test]
 fn timeline_rename_commits_on_enter_and_on_click_away() {
     // The rename field (double-click a name, or Enter on a selected layer) used to grab the