var LevelWriteStream = require('level-writestream');

var db = level('/path/to/level/db/dir');
LevelWriteStream(db);

var ws = db.createWriteStream();
ws.write({key: 'A', value: 'B'}, function(err) {
  if (err) throw err;
});
 
source.pipe(ws);
 
ws.once('finish', function() {
  console.log('finished');
});