code: def add_lvl_to_ui(self, level, header):
          
          w = QtGui.QWidget(self)
          vbox = QtGui.QVBoxLayout()
          vbox.setContentsMargins(0, 0, 0, 0)
          w.setLayout(vbox)
          if header is not None:
              vbox.addWidget(header)
          vbox.addWidget(level)
          self.splitter.addWidget(w)
docs: Insert the level and header into the ui.
  
          :param level: a newly created level
          :type level: :class:`jukeboxcore.gui.widgets.browser.AbstractLevel`
          :param header: a newly created header
          :type header: QtCore.QWidget|None
          :returns: None
          :rtype: None
          :raises: None