diff --git a/app/controllers/events_controller.rb b/app/controllers/events_controller.rb
index 91c6d5f5d3..48f0eefc52 100644
--- a/app/controllers/events_controller.rb
+++ b/app/controllers/events_controller.rb
@@ -947,6 +947,18 @@ def sub_organizations
 
         send_data csv, filename: "#{@event.name}'s sub-organizations.csv", type: "text/csv", disposition: :attachment
       end
+
+      # Like the CSV, the XLSX export intentionally does not consider filters.
+      # Unlike the CSV, it includes every visible descendant (not just direct
+      # sub-organizations), rendered as a collapsible tree via row grouping.
+      format.xlsx do
+        send_data(
+          Event::SubOrganizationsExport.new(@event, descendant_ids: visible_descendant_ids).xlsx,
+          filename: "#{@event.name}'s sub-organizations.xlsx",
+          type: "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
+          disposition: :attachment
+        )
+      end
     end
 
   end
diff --git a/app/models/event/sub_organizations_export.rb b/app/models/event/sub_organizations_export.rb
new file mode 100644
index 0000000000..5ac14b5b69
--- /dev/null
+++ b/app/models/event/sub_organizations_export.rb
@@ -0,0 +1,74 @@
+# frozen_string_literal: true
+
+class Event
+  class SubOrganizationsExport
+    # Excel supports at most 7 levels of row grouping. Deeper descendants are
+    # still exported, they just share the deepest collapsible level.
+    MAX_OUTLINE_LEVEL = 7
+
+    def initialize(event, descendant_ids:)
+      @event = event
+      @descendant_ids = descendant_ids
+    end
+
+    def xlsx
+      io = StringIO.new
+      workbook = WriteXLSX.new(io)
+
+      bold = workbook.add_format(bold: 1)
+
+      worksheet = workbook.add_worksheet("Sub-organizations")
+      # Attach each group's collapse toggle to the parent row above it rather
+      # than the default summary row below.
+      worksheet.outline_settings(1, 0, 0, 0)
+      worksheet.set_column("A:A", 20)
+      worksheet.set_column("B:C", 40)
+      worksheet.set_column("D:D", 12)
+      worksheet.set_column("E:E", 30)
+
+      worksheet.write_row(0, 0, ["ID", "Name", "Slug", "Balance", "Tags"], bold)
+
+      @current_row = 1
+      children_of(@event.id).each { |subevent| write_subtree(worksheet, subevent, 0) }
+
+      workbook.close
+      io.string
+    end
+
+    private
+
+    def write_subtree(worksheet, event, depth)
+      tags_for_parent = event.scoped_tags.select { |tag| tag.parent_event_id == event.parent_id }
+
+      # write_string keeps user-provided values (e.g. a name starting with "=")
+      # from being interpreted as formulas.
+      worksheet.write_string(@current_row, 0, event.public_id)
+      worksheet.write_string(@current_row, 1, "#{"    " * depth}#{event.name}")
+      worksheet.write_string(@current_row, 2, event.slug)
+      worksheet.write_number(@current_row, 3, event.balance_v2_cents / 100.0)
+      worksheet.write_string(@current_row, 4, tags_for_parent.map(&:name).join(", "))
+
+      if depth.positive?
+        # Syntax: set_row(row, height, format, hidden, level, collapsed)
+        worksheet.set_row(@current_row, nil, nil, 0, depth.clamp(0, MAX_OUTLINE_LEVEL))
+      end
+
+      @current_row += 1
+
+      children_of(event.id).each { |child| write_subtree(worksheet, child, depth + 1) }
+    end
+
+    def children_of(parent_id)
+      children_by_parent_id[parent_id] || []
+    end
+
+    def children_by_parent_id
+      @children_by_parent_id ||= Event.where(id: @descendant_ids)
+                                      .includes(:scoped_tags)
+                                      .order(:name)
+                                      .group_by(&:parent_id)
+    end
+
+  end
+
+end
diff --git a/app/views/events/sub_organizations.html.erb b/app/views/events/sub_organizations.html.erb
index 06fd7a3262..6256a3cf92 100644
--- a/app/views/events/sub_organizations.html.erb
+++ b/app/views/events/sub_organizations.html.erb
@@ -9,9 +9,20 @@
 <h1 class="heading flex items-center gap-2 flex-col sm:flex-row border-0 mb-0">
   <span class="flex-grow">Sub-organizations</span>
   <div class="flex items-center gap-2">
-    <%= pop_icon_to "download",
-                    { format: :csv },
-                    class: "tooltipped tooltipped--w", "aria-label": "Download all as CSV" %>
+    <div data-controller="menu" data-menu-placement-value="bottom-end">
+      <button
+        type="button"
+        aria-label="Download"
+        class="tooltipped tooltipped--w pop menu__toggle menu__toggle--arrowless overflow-visible"
+        data-menu-target="toggle"
+        data-action="menu#toggle click@document->menu#close keydown@document->menu#keydown">
+        <%= inline_icon "download", size: 28 %>
+      </button>
+      <div class="menu__content menu__content--2 h5" data-menu-target="content">
+        <%= link_to "Download as CSV", { format: :csv }, target: :_blank %>
+        <%= link_to "Download tree as Excel", { format: :xlsx }, target: :_blank %>
+      </div>
+    </div>
     <%= link_to event_new_sub_organization_path(@event), class: "btn bg-success", data: { behavior: "modal_trigger", modal: "create" }, disabled: !policy(@event).create_sub_organization? do %>
       <%= inline_icon "plus" %>
       Create a sub-organization
diff --git a/spec/controllers/events_controller_spec.rb b/spec/controllers/events_controller_spec.rb
index f139d5947d..c2a9a52363 100644
--- a/spec/controllers/events_controller_spec.rb
+++ b/spec/controllers/events_controller_spec.rb
@@ -25,6 +25,15 @@ def sign_in_organizer_of(event)
     create_session(organizer, verified: true)
   end
 
+  # XLSX files are zip archives; cell text lives in the shared strings table.
+  def xlsx_entry(body, entry)
+    Zip::File.open_buffer(StringIO.new(body)).read(entry)
+  end
+
+  def xlsx_strings(body)
+    Nokogiri::XML(xlsx_entry(body, "xl/sharedStrings.xml")).css("si").map(&:text)
+  end
+
   describe "#index" do
     before do
       # This is required since creating event configs creates a monthly announcement for the event authored by the system user
@@ -246,6 +255,14 @@ def sign_in_organizer_of(event)
         expect(rows["Transparent Grandchild"]["ID"]).to eq(grandchild.public_id)
         expect(rows["Transparent Grandchild"]["Parent ID"]).to eq(transparent_sub.public_id)
       end
+
+      it "excludes private sub-organizations from the XLSX export", :aggregate_failures do
+        get(:sub_organizations, params: { event_id: parent.slug }, format: :xlsx)
+
+        strings = xlsx_strings(response.body)
+        expect(strings).to include("Transparent Subsidiary")
+        expect(strings).not_to include("Private Subsidiary")
+      end
     end
 
     context "with a hidden sub-organization" do
@@ -291,6 +308,20 @@ def sign_in_organizer_of(event)
         expect(response.body).to include("Transparent Sub-organization")
         expect(response.body).to include("Private Sub-organization")
       end
+
+      it "renders every descendant as a collapsible tree in the XLSX export", :aggregate_failures do
+        nested = create(:event, parent: transparent_sub, is_public: true, name: "Nested Subsidiary")
+        sign_in_organizer_of(parent)
+
+        get(:sub_organizations, params: { event_id: parent.slug }, format: :xlsx)
+
+        strings = xlsx_strings(response.body)
+        expect(strings).to include("Transparent Subsidiary", "Private Subsidiary")
+        # Nested descendants are indented under their parent...
+        expect(strings).to include("    #{nested.name}")
+        # ...and grouped so Excel renders them collapsible.
+        expect(xlsx_entry(response.body, "xl/worksheets/sheet1.xml")).to include('outlineLevel="1"')
+      end
     end
   end