How to sort and remove tuples with same first element and only keeping the first occurrence

Question

Support we have a list of tuples listeT:

ListeT=[(\'a\', 1), (\'x\',1) , (\'b\', 1), (\'b\', 1), (\'a\', 2), (\'a\',3), (\'c\', 6), (\'c\', 5),(\'e\', 6), (