T(n)=T(n/2)+n2 cost of each level of this tree?

I am confused about this. Can anyone do it substitution method?

T(n)=T(n/2)+n2

T(n)=T(n/2)+n2
=T(n/4)+(n/2)2+n2 (expand T(n/2))
=T(n/8)+(n/4)2+(n/2)2+n2 (expand T(n/4))
T(n)=n2+(n/2)2+(n/4)2+(n/8)2+⋯+(n/2lgn)2
=n2+n2/4+n2/16+n2/64+⋯