driver-legacy/src/main/com/mongodb/BulkWriteOperation.java
public void insert(final DBObject document) {
        isTrue("already executed", !closed);
        if (document.get(ID_FIELD_NAME) == null) {
            document.put(ID_FIELD_NAME, new ObjectId());
        }
        addRequest(new InsertRequest(document, collection.getObjectCodec()));
    }
public void insert(final DBObject document) {
        isTrue("already executed", !closed);
        if (document.get(ID_FIELD_NAME) == null) {
            document.put(ID_FIELD_NAME, new ObjectId());
        }
        addRequest(new InsertRequest(document, collection.getObjectCodec()));
    }
Add an insert request to the bulk operation

@param document the document to insert