How to order by a column with specific order in mysql?

Question

I have this table

name        level
Dion        Leader
Roy         Member
Gerald      Member
Boyz        Assistant
Jade        Member
Gulliver    Leader
Ananda      Assistant
Vervada     Member

I'd like to do ORDER BY in this table. So, the first that is show is Leader, then assistant, then member AND it's ordered by they name too.

The output I'm looking for:

name        level
Dion        Leader
Gulliver    Leader
Ananda      Assistant
Boyz        Assistant
Gerald      Member
Jade        Member
Roy         Member
Vervada     Member

my current query is (not give correct output though) :

SELECT name,level FROM t_user ORDER BY level='Leader' DESC, level='Assistant' DESC

Note: If possible, the query is has to be as light/fast as possible. Because the t_user has 5k++ rows.