db.user.drop();
for (var x = 0; x < 10000; x++) {
    db.user.insert({ x: x });
    if (!db.getMongo().useWriteCommands()) {
        db.runCommand({ getLastError: 1 });
    }
}

db.user.drop();
var bulk = db.user.initializeUnorderedBulkOp();
for (var x = 0; x < 10000; x++) {
    bulk.insert({ x: x });
}
bulk.execute();