Number of different trees with 8 nodes

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The number of $\color{red}{\text{ different trees with 8 nodes}}$ is:

  1. $256$
  2. $255$
  3. $248$
  4. $\color{blue}{\text{None of these}}$

My attempt:

Since, question does not about order of tree, so I assume that combinations of possible tree with connected. i.e,$\color{green}{\text{ $N^{N-2}=8^6$ should be answer.}}$

But, somewhere it explained as :

The number of trees with $n$ nodes is given by formula

$\color{#FF033E}{\text{$2^n - n = 2^8-8=256-8=248$}}$

Can you explain it, please?