Visual business process modelling can fulfil an important role to enable high-level specification of system interactions, improve system integration and support performance analysis. Existing modelling approaches typically use a workflow based method. Cobweb and labyrinth problems appear quickly when this type of notation is used to model a complex enterprise system with users having to deal with either very complex diagrams or many cross-diagram implicit relationships. In contrast, a tree based presentation can be very efficient for handling visual relationships. We present an overview of EML (Enterprise Modelling Language), a novel tree overlay-based visual specification for enterprise process modelling and its support tool. The highlight is its flexibility in modelling business processes using different layers. A service- oriented tree structure represents the system functional architecture. Business process modelling is constructed as an overlay on top of this service tree. By using a multi-layer structure, an enterprise system can be modelled with a variety of early aspects to satisfy design requirements. An Eclipse based software tool, MaramaEML has been developed to edit EML diagrams integrated with existing modelling languages such as BPMN and supports automatic generation of BPEL code.