[
    {
        id: 0,
        name: 'Global'
    },
    {
        id: 1,
        name: 'Africa',
        sub_regions: [
            {
                id: 2,
                name: "East Africa",
                countries: [
                    {
                        id: 3,
                        name: "Burundi"
                    },
                    {
                        id: 4,
                        name: "Comoros"
                    }
                ]
            }
        ]
    },
    {
        id: 5,
        name: "Asia",
    }
]

<select>
    <option>Global</option>
    <option>Africa</option>
    <option>Burundi</option>
    ..
</select>

<select>
    <option value="region.id" v-for="region in regions">region.name</option>
</select>