creating treeview json at code behind

I want to create json data at code behind which is like treeview components example at below;

I can parse like first one but I don't know how to generate others (for ex.; tree_data['for-sale']['additionalParameters'])

Sample Data

    var tree_data = {
        'for-sale': { name: 'For Sale', type: 'folder' },
        'vehicles': { name: 'Vehicles', type: 'folder' },
        'rentals': { name: 'Rentals', type: 'folder' },
        'real-estate': { name: 'Real Estate', type: 'folder' },
        'pets': { name: 'Pets', type: 'folder' },
        'tickets': { name: 'Tickets', type: 'item' },
        'services': { name: 'Services', type: 'item' },
        'personals': { name: 'Personals', type: 'item' }
    }

    tree_data['for-sale']['additionalParameters'] = {
        'children': {
            'appliances': { name: 'Appliances', type: 'item' },
            'arts-crafts': { name: 'Arts & Crafts', type: 'item' },
            'clothing': { name: 'Clothing', type: 'item' },
            'computers': { name: 'Computers', type: 'item' },
            'jewelry': { name: 'Jewelry', type: 'item' },
            'office-business': { name: 'Office & Business', type: 'item' },
            'sports-fitness': { name: 'Sports & Fitness', type: 'item' }
        }
    }

    tree_data['vehicles']['additionalParameters'] = {
        'children': {
            'cars': { name: 'Cars', type: 'folder' },
            'motorcycles': { name: 'Motorcycles', type: 'item' },
            'boats': { name: 'Boats', type: 'item' }
        }
    }

    tree_data['vehicles']['additionalParameters']['children']['cars']['additionalParameters'] = {
        'children': {
            'classics': { name: 'Classics', type: 'item' },
            'convertibles': { name: 'Convertibles', type: 'item' },
            'coupes': { name: 'Coupes', type: 'item' },
            'hatchbacks': { name: 'Hatchbacks', type: 'item' },
            'hybrids': { name: 'Hybrids', type: 'item' },
            'suvs': { name: 'SUVs', type: 'item' },
            'sedans': { name: 'Sedans', type: 'item' },
            'trucks': { name: 'Trucks', type: 'item' }
        }
    }

    tree_data['rentals']['additionalParameters'] = {
        'children': {
            'apartments-rentals': { name: 'Apartments', type: 'item' },
            'office-space-rentals': { name: 'Office Space', type: 'item' },
            'vacation-rentals': { name: 'Vacation Rentals', type: 'item' }
        }
    }

    tree_data['real-estate']['additionalParameters'] = {
        'children': {
            'apartments': { name: 'Apartments', type: 'item' },
            'villas': { name: 'Villas', type: 'item' },
            'plots': { name: 'Plots', type: 'item' }
        }
    }

    tree_data['pets']['additionalParameters'] = {
        'children': {
            'cats': { name: 'Cats', type: 'item' },
            'dogs': { name: 'Dogs', type: 'item' },
            'horses': { name: 'Horses', type: 'item' },
            'reptiles': { name: 'Reptiles', type: 'item' }
        }
    }