How to Add Taxonomy Vocabulary in Rules when User Registers
I have checked the rules and I couldn't find a Data Selector for user name. But if you are fine with achieving the same using custom code then you can use the following code.

function YOURMODULENAME_user_insert(&amp;$edit, $account, $category){
   $vocabulary = new stdClass();
   $vocabulary-&gt;name = $account-&gt;name;
   $vocabulary-&gt;machine_name = "tutor_".$account-&gt;uid;
   $vocabulary-&gt;hierarchy = 0;
   taxonomy_vocabulary_save($vocabulary);
}