How to populate documents with unlimited nested levels using mongoose

I'm designing a web application that manages organizational structure for parent and child companies. There are two types of companies: 1- Main company, 2 -Subsidiary company.The company can belong only to one company but can have a few child companies. My mongoose Schema looks like this:

var companySchema = new mongoose.Schema({
    companyName: {
        type: String,
        required: true
    },
    estimatedAnnualEarnings: {
        type: Number,
        required: true
    },
    companyChildren: [{type: mongoose.Schema.Types.ObjectId, ref: 'Company'}],
    companyType: {type: String, enum: ['Main', 'Subsidiary']}
})

module.exports = mongoose.model('Company', companySchema);

I store all my companies in one collection and each company has an array with references to its child companies. Then I want to display all companies as a tree(on client side). I want query all Main companies that populates their children and children populate their children and so on,with unlimited nesting level. How can I do that? Or maybe you know better approach. Also I need ability to view,add,edit,delete any company.

Now I have this:

router.get('/companies', function(req, res) {
    Company.find({companyType: 'Main'}).populate({path: 'companyChildren'}).exec(function(err, list) {
        if(err) {
            console.log(err);
        } else {
            res.send(list);
        }
    })
});

But it populates only one nested level. I appreciate any help