SOURCE

var map = L.map('map').setView([55.7364, 37.557], 16);
L.tileLayer('https://api.mapbox.com/styles/v1/{id}/tiles/{z}/{x}/{y}?access_token={accessToken}', {
        attribution: '',
        maxZoom: 18,
        id: 'mapbox/streets-v11',
        tileSize: 512,
        zoomOffset: -1,
        accessToken: 'pk.eyJ1IjoieGtxLW5pY2t5IiwiYSI6ImNrYWwza2dqeDBzZ2UycHBlMGkzMHZsdnAifQ.MnUoXOsykU4zAvmzFAurvg'
}).addTo(map);
const data = {
  "type": "MultiPolygon",
  "coordinates": [
    [
      [
        [143.648007, 50.7476],
        [144.654148, 48.976391],
        [143.173928, 49.306551],
        [143.648007, 50.7476]
      ]
    ],
    [
      [
        [22.731099, 54.327537],
        [20.892245, 54.312525],
        [19.66064, 54.426084],
        [22.731099, 54.327537]
      ]
    ]
  ]
}
const geo = L.geoJson(data);
console.log(geo.getBounds());
geo.addTo(map);
map.fitBounds(geo.getBounds());

<div id="map"></div>

#map {
  height: 100vh;
  width: 100vw;
}