PaperMC/paper-server/nms-patches/net/minecraft/world/level/block/BlockSapling.patch

--- a/net/minecraft/world/level/block/BlockSapling.java
+++ b/net/minecraft/world/level/block/BlockSapling.java
@@ -15,12 +15,21 @@
 import net.minecraft.world.phys.shapes.VoxelShape;
 import net.minecraft.world.phys.shapes.VoxelShapeCollision;
 
+// CraftBukkit start
+import org.bukkit.Location;
+import org.bukkit.TreeType;
+import org.bukkit.block.BlockState;
+import org.bukkit.craftbukkit.util.CraftLocation;
+import org.bukkit.event.world.StructureGrowEvent;
+// CraftBukkit end
+
 public class BlockSapling extends BlockPlant implements IBlockFragilePlantElement {
 
     public static final BlockStateInteger STAGE = BlockProperties.STAGE;
     protected static final float AABB_OFFSET = 6.0F;
     protected static final VoxelShape SHAPE = Block.box(2.0D, 0.0D, 2.0D, 14.0D, 12.0D, 14.0D);
     private final WorldGenTreeProvider treeGrower;
+    public static TreeType treeType; // CraftBukkit
 
     protected BlockSapling(WorldGenTreeProvider worldgentreeprovider, BlockBase.Info blockbase_info) {
         super(blockbase_info);
@@ -45,7 +54,32 @@
         if ((Integer) iblockdata.getValue(BlockSapling.STAGE) == 0) {
             worldserver.setBlock(blockposition, (IBlockData) iblockdata.cycle(BlockSapling.STAGE), 4);
         } else {
-            this.treeGrower.growTree(worldserver, worldserver.getChunkSource().getGenerator(), blockposition, iblockdata, randomsource);
+            // CraftBukkit start
+            if (worldserver.captureTreeGeneration) {
+                this.treeGrower.growTree(worldserver, worldserver.getChunkSource().getGenerator(), blockposition, iblockdata, randomsource);
+            } else {
+                worldserver.captureTreeGeneration = true;
+                this.treeGrower.growTree(worldserver, worldserver.getChunkSource().getGenerator(), blockposition, iblockdata, randomsource);
+                worldserver.captureTreeGeneration = false;
+                if (worldserver.capturedBlockStates.size() > 0) {
+                    TreeType treeType = BlockSapling.treeType;
+                    BlockSapling.treeType = null;
+                    Location location = CraftLocation.toBukkit(blockposition, worldserver.getWorld());
+                    java.util.List<BlockState> blocks = new java.util.ArrayList<>(worldserver.capturedBlockStates.values());
+                    worldserver.capturedBlockStates.clear();
+                    StructureGrowEvent event = null;
+                    if (treeType != null) {
+                        event = new StructureGrowEvent(location, treeType, false, null, blocks);
+                        org.bukkit.Bukkit.getPluginManager().callEvent(event);
+                    }
+                    if (event == null || !event.isCancelled()) {
+                        for (BlockState blockstate : blocks) {
+                            blockstate.update(true);
+                        }
+                    }
+                }
+            }
+            // CraftBukkit end
         }
 
     }