A dockable ui template with menu bar, using QWidget instead of QMainWindow

dockableWidget.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QWidget" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>280</width>
    <height>600</height>
   </rect>
  </property>
  <property name="sizePolicy">
   <sizepolicy hsizetype="Fixed" vsizetype="Preferred">
    <horstretch>0</horstretch>
    <verstretch>0</verstretch>
   </sizepolicy>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <layout class="QVBoxLayout" name="verticalLayout">
   <property name="leftMargin">
    <number>0</number>
   </property>
   <property name="topMargin">
    <number>0</number>
   </property>
   <property name="rightMargin">
    <number>0</number>
   </property>
   <property name="bottomMargin">
    <number>0</number>
   </property>
   <item>
    <widget class="QMenuBar" name="menubar">
     <widget class="QMenu" name="menuWhat">
      <property name="title">
       <string>what</string>
      </property>
      <addaction name="action1"/>
      <addaction name="action2"/>
      <addaction name="action"/>
     </widget>
     <widget class="QMenu" name="menuDo">
      <property name="title">
       <string>do</string>
      </property>
     </widget>
     <widget class="QMenu" name="menuI">
      <property name="title">
       <string>i</string>
      </property>
     </widget>
     <widget class="QMenu" name="menuDo_2">
      <property name="title">
       <string>do</string>
      </property>
     </widget>
     <addaction name="menuWhat"/>
     <addaction name="menuDo"/>
     <addaction name="menuI"/>
     <addaction name="menuDo_2"/>
    </widget>
   </item>
   <item>
    <widget class="QWidget" name="widget" native="true">
     <property name="sizePolicy">
      <sizepolicy hsizetype="Preferred" vsizetype="Expanding">
       <horstretch>0</horstretch>
       <verstretch>0</verstretch>
      </sizepolicy>
     </property>
     <layout class="QVBoxLayout" name="verticalLayout_2">
      <item>
       <widget class="QTabWidget" name="tabWidget">
        <widget class="QWidget" name="tab">
         <attribute name="title">
          <string>Tab 1</string>
         </attribute>
         <layout class="QVBoxLayout" name="verticalLayout_3">
          <item>
           <widget class="QPushButton" name="pushButton">
            <property name="text">
             <string>PushButton</string>
            </property>
           </widget>
          </item>
          <item>
           <widget class="QPushButton" name="pushButton_2">
            <property name="text">
             <string>PushButton</string>
            </property>
           </widget>
          </item>
          <item>
           <widget class="QPushButton" name="pushButton_3">
            <property name="text">
             <string>PushButton</string>
            </property>
           </widget>
          </item>
          <item>
           <widget class="QPushButton" name="pushButton_4">
            <property name="text">
             <string>PushButton</string>
            </property>
           </widget>
          </item>
          <item>
           <widget class="QPushButton" name="pushButton_5">
            <property name="text">
             <string>PushButton</string>
            </property>
           </widget>
          </item>
          <item>
           <widget class="QToolButton" name="toolButton">
            <property name="text">
             <string>...</string>
            </property>
           </widget>
          </item>
         </layout>
        </widget>
        <widget class="QWidget" name="tab_2">
         <attribute name="title">
          <string>Tab 2</string>
         </attribute>
        </widget>
       </widget>
      </item>
     </layout>
    </widget>
   </item>
   <item>
    <widget class="QStatusBar" name="statusbar"/>
   </item>
  </layout>
  <action name="action1">
   <property name="text">
    <string>1</string>
   </property>
  </action>
  <action name="action2">
   <property name="text">
    <string>2</string>
   </property>
  </action>
  <action name="action">
   <property name="text">
    <string>'</string>
   </property>
  </action>
 </widget>
 <resources/>
 <connections/>
</ui>