code: function(treeType) {
      if (treeType === 'app') {
        let trees = [this.app.trees.app];
  
        // Push any custom paths onto the trees array
        // to be linted.
        if (this.scssLintOptions.includePaths) {
          trees.push.apply(trees, this.scssLintOptions.includePaths);
        }
  
        const linted = trees.map(function(tree) {
          const filteredTreeToBeLinted = new Funnel(tree, { exclude: ['**/*.js'] });
          return new ScssLinter(mergeTrees([filteredTreeToBeLinted]), this.scssLintOptions);
        }, this);
  
        return mergeTrees(linted);
      }
    }
docs: /*
  Lint the application's styles
  tree and report errors to the
  user.
  
  @method lintTree
  
  @param {String} treeType
  Either 'app', 'tests', 'templates', or 'addon'.
  
  @return {Object}
  Tree to be merged.