opentelemetry-js: Nested Child spans are not getting parented correctly

Please answer these questions before submitting a bug report.

What version of OpenTelemetry are you using? 0.15.0

What version of Node are you using? v14.15.5

Please provide the code you used to setup the OpenTelemetry SDK : https://github.com/mnadeem/nodejs-opentelemetry-tempo

What did you do? Created Child Spans

const doSomeWorkInNewNestedSpan = (parentSpan) => {
    const childSpan = tracer.startSpan('doSomeWorkInNewNestedSpan', {
        parentSpan, attributes: { 'code.function' : 'doSomeWorkInNewNestedSpan' }
    });
    childSpan.setAttribute('code.filepath', "test2");
    //Do some work
    doSomeHeavyWork();
    childSpan.end();
}

If possible, provide a recipe for reproducing the error.: Follow the guidelines in https://github.com/mnadeem/nodejs-opentelemetry-tempo

What did you expect to see? Nested Child spans should be parented correctly

Something like this nested and stair cased (from https://github.com/mnadeem/boot-opentelemetry-tempo)

What did you see instead? Nested child spans are not parented correctly

Additional context

Add any other context about the problem here.