Output of evaluation metric for XGBoost - is it cumulative?
That reflects the performance of the boosting of the 10 trees together.
I do reccomend you this tutorial https://www.youtube.com/watch?v=sRktKszFmSk&amp;t=4s
Gradient boosting is well explained there.
Using as a predictor only the 10th tree will give you weird results, since it is fitted on the residual errors of the previous 9