mongodB: Select docs with identical values of two fields

Is it possible to find only those documents in a collections with same value in two given fields?

{
    _id:    fewSFDewvfG20df 
    start:  10
    end:    10
}

As here start and end have the same value, this document would be selected.

I think about something like...

Collection.find({ start: { $eq: end } })

... which wouldn't work, as end has to be a value.