I am trying to find out the average number of comparisons made by the Binary search. In that, I'm confronted with following summation :-
Avg = $(1/n)\sum_{i=1}^{\log_2 n} i*2^i$
In this summation, $i$ are the number of comparisons made at each node in $i^{th}$ level of the Binary tree and $2^i$ is the number of nodes in the tree at level $i$.
Please help me solve this summation. If not completely solve the summation, at least please help me get started.