diff --git a/tests/gtk/test_tree.py b/tests/gtk/test_tree.py
index 4aa2cb0..09a4536 100644
--- a/tests/gtk/test_tree.py
+++ b/tests/gtk/test_tree.py
@@ -193,3 +193,77 @@ class TestDateDeviceList(unittest.TestCase):
 
         with self.assertRaises(IndexError):
             self.assertIsNone(tree[5])
+
+
+class TestTagDeviceList(unittest.TestCase):
+    """Test case for our TagDeviceList GObject."""
+
+    def setUp(self):
+        """Set up common variables."""
+        self.tag = xfstestsdb.gtk.tree.TagDeviceList(name="mytag")
+
+    def test_init(self):
+        """Test creating a TagDeviceList instance."""
+        self.assertIsInstance(self.tag, GObject.GObject)
+        self.assertIsInstance(self.tag, Gio.ListModel)
+        self.assertEqual(self.tag.name, "mytag")
+        self.assertEqual(str(self.tag), "mytag")
+
+    def test_lt(self):
+        """Test comparing TagDeviceList instances."""
+        tag_a = xfstestsdb.gtk.tree.TagDeviceList(name="a")
+        tag_b = xfstestsdb.gtk.tree.TagDeviceList(name="b")
+
+        now = datetime.datetime.now()
+        then = now - datetime.timedelta(seconds=42)
+        tag_a.add_run(1, "/dev/vda1", now)
+        tag_b.add_run(2, "/dev/vda2", then)
+
+        self.assertTrue(tag_a < tag_b)
+        self.assertFalse(tag_b < tag_a)
+        self.assertFalse(tag_a < tag_a)
+
+        tag_a.add_run(2, "/dev/vda2", then)
+        self.assertTrue(tag_b < tag_a)
+
+    def test_get_item_type(self):
+        """Test the get_item_type() function."""
+        self.assertEqual(self.tag.get_item_type(),
+                         xfstestsdb.gtk.tree.DeviceRunsList.__gtype__)
+
+    def test_get_n_items(self):
+        """Test the get_n_items() function."""
+        self.assertEqual(self.tag.get_n_items(), 0)
+        self.assertEqual(self.tag.n_items, 0)
+
+        self.tag.add_run(1, "/dev/vda1", datetime.datetime.now())
+        self.assertEqual(self.tag.get_n_items(), 1)
+        self.assertEqual(self.tag.n_items, 1)
+
+    def test_get_item(self):
+        """Test the get_item() function."""
+        now = datetime.datetime.now()
+        then = now - datetime.timedelta(seconds=42)
+
+        self.tag.add_run(1, "/dev/vda2", now)
+        self.assertIsInstance(self.tag[0], xfstestsdb.gtk.tree.DeviceRunsList)
+        self.assertEqual(self.tag[0].name, "/dev/vda2")
+        self.assertEqual(self.tag[0][0].runid, 1)
+        self.assertEqual(self.tag[0][0].timestamp, now)
+        self.assertEqual(self.tag[0][0].ftime, "%c")
+
+        self.tag.add_run(2, "/dev/vda1", then)
+        self.assertEqual(self.tag[0].name, "/dev/vda1")
+        self.assertEqual(self.tag[1].name, "/dev/vda2")
+
+    def test_get_earliest_run(self):
+        """Test the get_earliest_run() function."""
+        self.assertIsNone(self.tag.get_earliest_run())
+
+        now = datetime.datetime.now()
+        self.tag.add_run(1, "/dev/vda1", now)
+        self.assertEqual(self.tag.get_earliest_run().runid, 1)
+
+        then = now - datetime.timedelta(seconds=42)
+        self.tag.add_run(2, "/dev/vda2", then)
+        self.assertEqual(self.tag.get_earliest_run().runid, 2)
diff --git a/xfstestsdb/gtk/tree.py b/xfstestsdb/gtk/tree.py
index 07f3e7e..6c537f9 100644
--- a/xfstestsdb/gtk/tree.py
+++ b/xfstestsdb/gtk/tree.py
@@ -126,3 +126,57 @@ class DateDeviceList(GObject.GObject, Gio.ListModel):
         min = datetime.datetime.combine(date, datetime.time())
         max = min + datetime.timedelta(days=1)
         return (min, max)
+
+
+class TagDeviceList(GObject.GObject, Gio.ListModel):
+    """Contains a single tag with multiple devices and runs."""
+
+    name = GObject.Property(type=str)
+    n_items = GObject.Property(type=int)
+
+    def __init__(self, name: str) -> None:
+        """Initialize our TagDeviceList."""
+        super().__init__(name=name)
+        self.__devices = []
+
+    def __lt__(self, rhs: typing.Self) -> bool:
+        """Compare two TagDeviceList objects."""
+        lhs_run = self.get_earliest_run()
+        rhs_run = rhs.get_earliest_run()
+        if lhs_run.runid == rhs_run.runid:
+            return self.name > rhs.name
+        return lhs_run > rhs_run
+
+    def __str__(self) -> str:
+        """Get the name of this tag."""
+        return self.name
+
+    def do_get_item_type(self) -> GObject.GType:
+        """Get the type of objects in the list."""
+        return DeviceRunsList.__gtype__
+
+    def do_get_n_items(self) -> int:
+        """Get the number of devices added to this tag."""
+        return self.n_items
+
+    def do_get_item(self, n: int) -> DeviceRunsList:
+        """Get the device at the nth position."""
+        return self.__devices[n]
+
+    def add_run(self, runid: int, device: str,
+                timestamp: datetime.datetime) -> None:
+        """Add a run to the Tag's list."""
+        pos = bisect.bisect_left(self.__devices, device, key=str)
+        if pos < len(self.__devices) and self.__devices[pos].name == device:
+            dev = self.__devices[pos]
+        else:
+            dev = DeviceRunsList(device)
+            self.__devices.insert(pos, dev)
+
+        dev.add_run(runid, timestamp, "%c")
+        self.n_items = len(self.__devices)
+
+    def get_earliest_run(self) -> XfstestsRun | None:
+        """Get the earliest run added to the tag."""
+        runs = [d.get_earliest_run() for d in self.__devices]
+        return min(runs, default=None)