Hi Nishant,
you did not specify in which aggregation the button needs to be shown.
Make sure to wrap either one of the following around your second button:
<contentLeft></contentLeft>
<contentMiddle></contentMiddle>
<contentRight></contentRight>
So your code will be:
<Bar id="searc">
<contentRight>
<Button type="Back"/>
</contentRight>
</Bar>
See also SAPUI5 SDK - Demo Kit
Regards,
Dominik