Who can initiate an optional referendum at the national level?

Burundi
Burundi'sConstitution of 2005
https://www.constituteproject.org/constitution/Burundi_2005.pdf
Article198
ThePresident of the Republic may, after consultation with the Vice-Presidents ofthe
Republic,with the President of the National Assembly and with the President of the
Senate,submit to a referendum any draft of a constitutional, legislative or othertext, susceptible of having profound repercussions on the life and the futureof the Nation or on the nature or the functioning of the institutions of theRepublic.