private static DataFlavor createLocalGroupFlavor() {
        try {
            return new DataFlavor(
                DataFlavor.javaJVMLocalObjectMimeType+
                "; class="+Group.class.getName(), 
                "Local Group");
            
        }catch (Exception e) {
            Msg.showError(GroupTransferable.class, null, null, null, e);
        }
        return null;
    }
A test implementation of data that could be dragged onto the ProgramTree.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/programtree/GroupTransferable.java