_getDistribution() {
    const distribution = {};
    let nodeId, node;

    // we fix Y because the hierarchy is vertical,
    // we fix X so we do not give a node an x position for a second time.
    // the fix of X is removed after the x value has been set.
    for (nodeId in this.body.nodes) {
      if (Object.prototype.hasOwnProperty.call(this.body.nodes, nodeId)) {
        node = this.body.nodes[nodeId];
        const level =
          this.hierarchical.levels[nodeId] === undefined
            ? 0
            : this.hierarchical.levels[nodeId];
        this.direction.fix(node, level);
        if (distribution[level] === undefined) {
          distribution[level] = {};
        }
        distribution[level][nodeId] = node;
      }
    }
    return distribution;
  }
This function get the distribution of levels based on hubsize
@returns {object}
@private