You need to specify 'Publish WSDL' options and create the WSDL accordingly. If Publish WSDL options are not specified it will show only the mediate operation.
Read the following docs to know more about this.
http://maharachchi.blogspot.com/2013/07/publishwsdl-option-in-wso2-esb-explained.html
EDIT - You can specify the format attribute as SOAP 1.2 in the endpoint in your proxy configuration to convert all requests to SOAP 1.2. Sample Proxy config is as follows
<proxy xmlns="http://ws.apache.org/ns/synapse" name="EchoProxy" transports="https,http" statistics="disable" trace="disable"
startOnLoad="true">
<target>
<outSequence>
<send/>
</outSequence>
<endpoint>
<address uri="http://localhost:8280/services/echo" format="soap12"/>
</endpoint>
</target>
<publishWSDL uri="http://localhost:8282/services/echo?wsdl"/>
<description/>
</proxy>