postgresql array query (cannot accumulate arrays of different dimensionality)

Question

select * from temp10

k    v
ㅡㅡㅡㅡㅡㅡ
a   {a,b}
a   {c}
b   {d,e}
b   {f}

to

k    v
ㅡㅡㅡㅡㅡㅡ
a   {a,b,c}
b   {d,e,f}

I want these results.

my t