<xs:schema targetNamespace="cp:level" xmlns="cp:level" xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="Level">
    <xs:complexType>
      <xs:sequence>
        <xs:element ref="Balloons"/>
      </xs:sequence>
    </xs:complexType>    
  </xs:element>

  <xs:element name="Balloons">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="BalloonGroupTemplates" minOccurs="0" maxOccurs="1">
          <xs:complexType>
            <xs:sequence>
              <xs:element name="BalloonGroupTemplate" type="BalloonGroupTemplateType" minOccurs="0"/>
            </xs:sequence>
          </xs:complexType>
        </xs:element>
        <xs:element name="BalloonSequence">
          <xs:complexType>
            <xs:sequence minOccurs="0" maxOccurs="unbounded">
              <xs:element name="Balloon" type="BalloonType" minOccurs="0" maxOccurs="unbounded" />
              <xs:element name="BalloonGroup" type="BalloonGroupType" minOccurs="0" maxOccurs="unbounded"/>
            </xs:sequence>
          </xs:complexType>
         </xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>


  <xs:complexType name="BalloonGroupTemplateType">
    <!-- не так важно -->
  </xs:complexType>

  <xs:complexType name="BalloonGroupType">
    <!-- не так важно -->
  </xs:complexType>

  <xs:complexType name="BalloonType">
    <!-- не так важно -->
  </xs:complexType>
</xs:schema>

<Level xmlns="cp:level">
  <Balloons>
    <BalloonGroupTemplates xmlns="">
      <BalloonGroupTemplate name="bgtname1">
        <Balloon name="bname1"/>
      </BalloonGroupTemplate>
    </BalloonGroupTemplates>
    <BalloonSequence xmlns="">
    </BalloonSequence>
  </Balloons>
</Level>