mongodb instrumentation: nested span is not generated when using callback

[AndriyPashchak]

What version of OpenTelemetry are you using?

"@opentelemetry/api": "0.18.0"
"@opentelemetry/core": "0.18.0"
"@opentelemetry/instrumentation-mongodb": "0.14.0"

What version of Node are you using?

12.20.0

What did you do?

import { SimpleSpanProcessor } from '@opentelemetry/tracing';
import { NodeTracerProvider } from '@opentelemetry/node';
import { ZipkinExporter } from '@opentelemetry/exporter-zipkin';

import { registerInstrumentations } from '@opentelemetry/instrumentation';
import { HttpInstrumentation } from '@opentelemetry/instrumentation-http';
import { MongoDBInstrumentation } from '@opentelemetry/instrumentation-mongodb';

const serviceName = 'otel-mongodb-test';

const provider = new NodeTracerProvider();

registerInstrumentations({
    instrumentations: [
        new HttpInstrumentation(),
        new MongoDBInstrumentation(),
    ],
    tracerProvider: provider,
});

const zipkinExporter = new ZipkinExporter({
    serviceName,
    url: 'http://localhost:9411/api/v2/spans'
});

provider.addSpanProcessor(new SimpleSpanProcessor(zipkinExporter));
provider.register();
const tracer = provider.getTracer(serviceName);

import * as http from 'http';
import * as mongodb from 'mongodb';

let collection;
const mongodbConnect = async () => {
    try {
        const client = await mongodb.MongoClient.connect('mongodb://localhost:27017');
        collection = client.db('test-db').collection('users');
        console.log('\nSuccessfully connected to mongoDB!\n');
    } catch (err) {
        console.log(`Error while connecting to mongoDB ${err}`, err);
        throw err;
    }
};

mongodbConnect();

http.createServer(function (_, res) {
    const doc = { name: 'Rick' };

    collection.insertOne(doc, function () {
        collection.findOne({}, function () {
            res.end();
        });
    });
}).listen(9090);

What did you expect to see?

The new mongodb.find span being generated as a child of the mongodb.insert span.

What did you see instead?

Additional context

It happens when a callback for a parent mongodb.insert operation is used.

When I'm using Promise.then instead of a callback a span for a find operation is generated as expected.

The following example works fine:

collection.insertOne(doc).then(function () {
        collection.findOne({}, function () {
            res.end();
        });
    });