There is at least one tree (OBJECT_WORLDTREE) that is already an object. I would think you can find it using cbox and add as many as you want to the region you like. To make them look different I set them at different heights. You can probably rotate them to make them look even more unique.
Here is a copse I added to Bleach Bone Island:
scriptNewThing Object;
Player 4;
UID 18446741874686296065;
DefinitionType "OBJECT_WORLDTREE";
ScriptName NULL;
ScriptData "NULL";
ThingGamePersistent FALSE;
ThingLevelPersistent FALSE;
Health 1.00000;
ObjectScale 1.00000;
StartCTCPhysicsStandard;
PositionX 23.16841;
PositionY 23.89404;
PositionZ 5.12961;
RHSetForwardX 0.40673;
RHSetForwardY 0.91355;
RHSetForwardZ 0.00000;
RHSetUpX 0.00000;
RHSetUpY 0.00000;
RHSetUpZ 1.00000;
EndCTCPhysicsStandard;
StartCTCEditor;
LockedInPlace FALSE;
AttachToGround TRUE;
Freezed FALSE;
EndCTCEditor;
EndThing;