How would you create an invoice with multiple lines?

[BillBrower]

The example code for invoices is straight forward for single line invoices. But since lines is a js object and you can't have duplicate keys I don't see a clear way to create an invoice with multiple lines. Could you shed some light on this?

var Freshbooks = require('freshbooks-node');
var freshbooks = new Freshbooks(APPLICATION_NAME, APPLICATION_TOKEN, USER_AGENT)
freshbooks.call('invoice.create',
    {
        invoice:
        {   client_id: 32,
            status: 'draft',
            lines: {
                line:
                {
                    name: 'Tulips',
                    description: 'A type of flower',
                    unit_cost: 10,
                    quantity: 2
                }
            }
        }
    }, function(err, json) {
        if (err) {
            console.error(err);
        }
        console.log(JSON.stringify(json, null, 4));
    });