diff --git a/cura/Machines/ContainerTree.py b/cura/Machines/ContainerTree.py
index 30c9b8f90d..ebb957b5f7 100644
--- a/cura/Machines/ContainerTree.py
+++ b/cura/Machines/ContainerTree.py
@@ -1,6 +1,9 @@
 # Copyright (c) 2019 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
 
+from UM.Settings.ContainerRegistry import ContainerRegistry  # To listen to containers being added.
+from UM.Settings.DefinitionContainer import DefinitionContainer
+from UM.Settings.Interfaces import ContainerInterface
 from cura.Machines.MachineNode import MachineNode
 
 from typing import Dict
@@ -12,4 +15,15 @@ from typing import Dict
 #   there will be one machine node here.
 class ContainerTree:
     def __init__(self) -> None:
-        self.machines = {}  # type: Dict[str, MachineNode] # Mapping from definition ID to machine nodes.
\ No newline at end of file
+        self.machines = {}  # type: Dict[str, MachineNode] # Mapping from definition ID to machine nodes.
+        ContainerRegistry.getInstance().containerAdded.connect(self.machineAdded)
+
+    ##  When a printer gets added, we need to build up the tree for that container.
+    def machineAdded(self, definition_container: ContainerInterface):
+        if not isinstance(definition_container, DefinitionContainer):
+            return  # Not our concern.
+        definition_id = definition_container.getId()
+        if definition_id in self.machines:
+            return  # Already have this definition ID.
+
+        self.machines[definition_id] = MachineNode(definition_id)
\ No newline at end of file