--project-tree this argument is used when GroIMP is run in Eclipse, it tells GroIMP to load classes under the local /PLUGIN/target/classes/ repositories where PLUGIN is the name of each directories at the root of GroIMP. This path is different when GroIMP is run after packaging. By default GroIMP load classes in ./plugins/PLUGIN/PLUGIN.jar where PLUGIN is the name of each plugins.