Add parent_tree_url to TreeRootEntity and tree_path to blob JSON

app/controllers/projects/blob_controller.rb

@@ -198,6 +198,10 @@ class Projects::BlobController < Projects::ApplicationController
     json = blob_json(@blob)
     return render_404 unless json
 
+    path_segments = @path.split('/')
+    path_segments.pop
+    tree_path = path_segments.join('/')
+
     render json: json.merge(
       path: blob.path,
       name: blob.name,
@@ -212,6 +216,7 @@ class Projects::BlobController < Projects::ApplicationController
       raw_path: project_raw_path(project, @id),
       blame_path: project_blame_path(project, @id),
       commits_path: project_commits_path(project, @id),
+      tree_path: project_tree_path(project, File.join(@ref, tree_path)),
       permalink: project_blob_path(project, File.join(@commit.id, @path))
     )
   end

app/serializers/tree_root_entity.rb

 # TODO: Inherit from TreeEntity, when `Tree` implements `id` and `name` like `Gitlab::Git::Tree`.
 class TreeRootEntity < Grape::Entity
-  expose :path
+  include RequestAwareEntity
   
+  expose :path
+
   expose :trees, using: TreeEntity
   expose :blobs, using: BlobEntity
   expose :submodules, using: SubmoduleEntity
+
+  expose :parent_tree_url do |tree|
+    next unless tree.path.present?
+
+    path_segments = tree.path.split('/')
+    path_segments.pop
+    parent_tree_path = path_segments.join('/')
+
+    project_tree_path(request.project, File.join(request.ref, parent_tree_path))
+  end
 end