diff --git a/tree.yml b/tree.yml
index 83bf644391d..801c932e8e4 100644
--- a/tree.yml
+++ b/tree.yml
@@ -155,6 +155,7 @@ advRocketry:
     - liquidEngine
     - solidBooster
     - solidBooster1-1
+    - M55
 
 scienceTech:
 
@@ -173,6 +174,9 @@ spaceExploration:
 landing:
 
 heavyRocketry:
+    - solidBooster1-1Small
+# NOTE: This ^^ is going to change to a Castor 1, and be moved to advRocketry.
+    - 
 
 fuelSystems:
 
@@ -187,6 +191,9 @@ advElectrics:
 specializedControl:
 
 heavierRocketry:
+    - engineLargeSkipper_125m
+    - liquidEngineMiniRescale
+    - solidBoosterSmall
 
 specializedConstruction: