code: function (polygons) {
      // new polygons can only be added to root node; children can only be splitted polygons
      if (!this.isRootNode()) {
        throw new Error('Assertion failed')
      }
      let _this = this
      polygons.map(function (polygon) {
        _this.addChild(polygon)
      })
    }
docs: fill the tree with polygons. Should be called on the root node only; child nodes must always be a derivate (split) of the parent node.