toTree(additionalTrees) {
    let packagedTree;

    let fullTree = mergeTrees(this.toArray(), {
      overwrite: true,
      annotation: 'Full Application',
    });

    fullTree = this._debugTree(fullTree, 'prepackage');

    if (!packagedTree) {
      packagedTree = this._legacyPackage(fullTree);
    }

    let trees = [].concat(packagedTree, additionalTrees).filter(Boolean);
    let combinedPackageTree = broccoliMergeTrees(trees);

    return this.addonPostprocessTree('all', combinedPackageTree);
  }
Returns the merged tree for this application

    @public
    @method toTree
    @param  {Array} [additionalTrees] Array of additional trees to merge
    @return {Tree}                  Merged tree for this application