When to Use Tree DP

These are the signs of Tree DP problems:

$1.$ Definitely, when we have tree structure. Vertices are connected without cycles.

$2.$ Aggregate computation. Answers depend on combining subtree results.

$3.$ Path or subtree properties. Maximum path, counting configurations, distance sums.

The state is typically $dp[v]$ representing the answer for the subtree rooted at $v$. For re-rooting problems, you'll have $dp[v]$ when $v$ is the root.