kate editor (default kate package on Ubuntu 14.04).
I found an option in View menu, but it doesn't work as needed.
I'm one of the Kate developers: Folding toplevel nodes should work as expected through the menu View > Code Folding > Fold Toplevel Nodes.
In the upcoming KDE Frameworks 5.27 release, KTextEditor will additionally have the entry View > Code Folding > Unfold Toplevel Nodes, see this commit.
So right now, you have to wait for the next KDE Frameworks update, which will be released mid of October 2016.
PS: Ubuntu 14.04 is really old. You should consider updating to a more recent version of KDE, best Plasma 5.8 which has long term support (LTS).