for each node v,calculate a(v)-maximum cost achieved by the subtree with root "v" in which v will attend, and n(v)-maximum cost achived by the subtree with root "v" in which v will not attend.
a(v)=p(v)+n(v1)+n(v2)+...+n(vn), vi-is the child of v.,p(v)-is the point of v itself.
n(v)=sum(max(n(vi),a(vi))),for all i-s.
and simply use DFS.

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