In order to fulfil the model instance from the root, you can get advantage of: the hierarchical representation in a tree shape that shows the Tree Viewer and of the mechanisms that EMF includes in this type of viewers.
It is as easy as put yourself in any point of the tree and display the pop-up menu with the right click. In the case of the tree node is a container of other elements, it will appear the option New Child. It will permit us to create sons of this node (of a specific class). For example, you can create nodes of Model class as sons of the OCLEditor root. At the same time, these Model nodes will be able to have nodes of Context class as sons, etc., following the aggregation relations that appear in the persistent model of the OCLEditor (have a look at Figure).
OCL Editor model.
Next figure shows an instance fully fulfilled.