Answer
$128=2^7$
Work Step by Step
$\ \ 128$
$\swarrow\searrow$
$2\ \ \ \ 64$
$\ \ \ \swarrow\searrow$
$\ \ \ 2\ \ \ \ \ \ \ 32$
$\ \ \ \ \ \ \ \ \ \swarrow\searrow$
$\ \ \ \ \ \ \ \ \ 2\ \ \ \ \ \ \ 16$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \swarrow\searrow$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ 2\ \ \ \ \ \ \ 8$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \swarrow\searrow$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 2\ \ \ \ \ \ \ 4$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \swarrow\searrow$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 2\ \ \ \ \ \ \ 2$