diff --git a/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.cpp b/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.cpp
index f394c8b..e1c23a3 100644
--- a/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.cpp
+++ b/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.cpp
@@ -74,7 +74,7 @@ constexpr ox::Point fbPtToTileAddr(
 }
 
 WorldEditorImGui::WorldEditorImGui(studio::Context &sctx, ox::StringParam path):
-		Editor(sctx, std::move(path)),
+		Editor{sctx, std::move(path)},
 		m_sctx{sctx},
 		m_objSetPicker{"Object Set Chooser", keelCtx(m_sctx), FileExt_jwob},
 		m_doc{*keel::readObj<WorldDoc>(keelCtx(m_sctx), itemPath()).unwrapThrow()} {
@@ -88,6 +88,7 @@ WorldEditorImGui::WorldEditorImGui(studio::Context &sctx, ox::StringParam path):
 			keelCtx(m_sctx), itemPath(), [this](WorldEditorConfig const&config) {
 				m_view.setAnimate(config.animateBg);
 			});
+	undoStack()->changeTriggered.connect(this, &WorldEditorImGui::handleUndoStackChange);
 }
 
 void WorldEditorImGui::draw(studio::Context&) noexcept {
@@ -187,23 +188,57 @@ ox::Error WorldEditorImGui::saveItem() noexcept {
 	return m_sctx.project->writeObj(itemPath(), m_doc, ox::ClawFormat::Organic);
 }
 
-void WorldEditorImGui::drawObjSetSelector() noexcept {
-	ig::IDStackItem const idStackItem("ObjSetSelector");
+void WorldEditorImGui::drawObjSelector() noexcept {
+	ig::IDStackItem const idStackItem("ObjSelector");
 	if (ig::PushButton("+", SqrBtnSize)) {
 		m_objSetPicker.open();
 	}
 	ImGui::SameLine();
+	ImGui::BeginDisabled(m_objMgr.selectedObjSet.len() == 0);
 	if (ig::PushButton("-", SqrBtnSize)) {
 		rmObjSet();
 	}
-	ig::ListBox("Object Sets", [this](size_t i) -> ox::CStringView {
-		auto const&uuidUrl = m_doc.objSets[i].path;
-		auto [setName, err] = uuidUrlToPath(keelCtx(m_sctx), uuidUrl);
-		if (err) {
-			setName = uuidUrl;
+	ImGui::EndDisabled();
+	ImGui::BeginChild("ObjTree");
+	{
+		for (auto const&[uuidUrl, setId, set] : m_objSets) {
+			auto flags = ImGuiTreeNodeFlags_OpenOnArrow | ImGuiTreeNodeFlags_OpenOnDoubleClick;
+			auto [setName, err] = uuidUrlToPath(keelCtx(m_sctx), uuidUrl);
+			auto const uuid = substr(uuidUrl, 7);
+			if (err) {
+				setName = uuidUrl;
+			}
+			if (uuid == m_objMgr.selectedObjSet) {
+				flags |= ImGuiTreeNodeFlags_Selected;
+			}
+			if (ImGui::TreeNodeEx(setName.c_str(), flags)) {
+				if (ImGui::IsItemClicked()) {
+					m_objMgr.selectedObjSet = uuid;
+				}
+				for (auto const&obj : set->objects) {
+					if (ImGui::TreeNodeEx(obj.name.c_str(), ImGuiTreeNodeFlags_Leaf)) {
+						if (ImGui::IsItemHovered() && ImGui::IsMouseDoubleClicked(ImGuiMouseButton_Left)) {
+							studio::navigateTo(m_sctx, setName, obj.name);
+						}
+						ImGui::TreePop();
+					}
+					ig::dragDropSource([&] {
+						std::ignore = ig::setDragDropPayload("WorldTile", WorldTileDragDrop{
+							.setId = setId,
+							.objId = obj.id,
+						});
+						ImGui::Text("%s", obj.name.c_str());
+					});
+				}
+				ImGui::TreePop();
+			} else {
+				if (ImGui::IsItemClicked()) {
+					m_objMgr.selectedObjSet = uuid;
+				}
+			}
 		}
-		return setName;
-	}, m_doc.objSets.size(), m_palMgr.selectedIdx);
+	}
+	ImGui::EndChild();
 	if (ig::DragDropTarget const d; d) {
 		auto const [fr, err] = ig::getDragDropPayload<studio::FileRef>("FileRef");
 		if (!err && endsWith(fr.path, FileExt_jwob)) {
@@ -212,35 +247,6 @@ void WorldEditorImGui::drawObjSetSelector() noexcept {
 	}
 }
 
-void WorldEditorImGui::drawObjSelector() noexcept {
-	ig::IDStackItem const idStackItem("ObjSelector");
-	for (auto const&[uuidUrl, setId, set] : m_objSets) {
-		constexpr auto flags = ImGuiTreeNodeFlags_OpenOnArrow | ImGuiTreeNodeFlags_OpenOnDoubleClick;
-		auto [setName, err] = uuidUrlToPath(keelCtx(m_sctx), uuidUrl);
-		if (err) {
-			setName = uuidUrl;
-		}
-		if (ImGui::TreeNodeEx(setName.c_str(), flags)) {
-			for (auto const&obj : set->objects) {
-				if (ImGui::TreeNodeEx(obj.name.c_str(), ImGuiTreeNodeFlags_Leaf)) {
-					if (ImGui::IsItemHovered() && ImGui::IsMouseDoubleClicked(ImGuiMouseButton_Left)) {
-						studio::navigateTo(m_sctx, setName, obj.name);
-					}
-					ImGui::TreePop();
-				}
-				ig::dragDropSource([&] {
-					std::ignore = ig::setDragDropPayload("WorldTile", WorldTileDragDrop{
-						.setId = setId,
-						.objId = obj.id,
-					});
-					ImGui::Text("%s", obj.name.c_str());
-				});
-			}
-			ImGui::TreePop();
-		}
-	}
-}
-
 void WorldEditorImGui::drawPropEditor() noexcept {
 	if (m_sizeEditor.show) {
 		constexpr auto popupSz = ImVec2{285, 0};
@@ -285,7 +291,6 @@ void WorldEditorImGui::drawMenu() noexcept {
 
 void WorldEditorImGui::drawResources() noexcept {
 	ig::IDStackItem const idStackItem("Resources");
-	drawObjSetSelector();
 	drawObjSelector();
 }
 
@@ -399,7 +404,13 @@ ox::Error WorldEditorImGui::addObjSet(ox::StringViewCR path) noexcept {
 }
 
 void WorldEditorImGui::rmObjSet() noexcept {
-	std::ignore = pushCommand<RmObjectSet>(m_doc, m_palMgr.selectedIdx);
+	auto const idx = ox::find_if(
+		m_doc.objSets.begin(), m_doc.objSets.end(), [this](ObjectSetEntry const &e) {
+			return substr(e.path, 7) == m_objMgr.selectedObjSet;
+		});
+	if (idx != m_doc.objSets.end()) {
+		std::ignore = pushCommand<RmObjectSet>(m_doc, idx.offset());
+	}
 }
 
 ox::Error WorldEditorImGui::handleDepUpdate(ox::StringViewCR, ox::UUID const&uuid) noexcept {
@@ -458,4 +469,14 @@ ox::Error WorldEditorImGui::addDependency(ox::FileAddress const&fileAddr) noexce
 	return {};
 }
 
+ox::Error WorldEditorImGui::handleUndoStackChange(studio::UndoCommand const*cmd) noexcept {
+	if (dynamic_cast<AddObjectSet const*>(cmd)) {
+		return loadObjectSets();
+	}
+	if (dynamic_cast<RmObjectSet const*>(cmd)) {
+		return loadObjectSets();
+	}
+	return {};
+}
+
 }
diff --git a/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.hpp b/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.hpp
index 7f1db39..ee35259 100644
--- a/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.hpp
+++ b/src/jasper/modules/world/src/studio/worldeditor/worldeditor-imgui.hpp
@@ -40,8 +40,8 @@ class WorldEditorImGui: public studio::Editor {
 		WorldStaticLoader m_loader{keelCtx(m_sctx), m_worldStatic, m_doc};
 		WorldEditorView m_view{m_sctx, m_worldStatic};
 		struct {
-			size_t selectedIdx{};
-		} m_palMgr;
+			ox::UUIDStr selectedObjSet;
+		} m_objMgr;
 		struct {
 			bool show{};
 			int columns{};
@@ -67,8 +67,6 @@ class WorldEditorImGui: public studio::Editor {
 		ox::Error saveItem() noexcept final;
 
 	private:
-		void drawObjSetSelector() noexcept;
-
 		void drawObjSelector() noexcept;
 
 		void drawPropEditor() noexcept;
@@ -101,6 +99,8 @@ class WorldEditorImGui: public studio::Editor {
 
 		ox::Error addDependency(ox::FileAddress const&fileAddr) noexcept;
 
+		ox::Error handleUndoStackChange(studio::UndoCommand const*) noexcept;
+
 		[[nodiscard]]
 		constexpr bool popupOpen() const noexcept {
 			return m_sizeEditor.show;