[FEA] Obtaining individual tree results of a random forest

[YuelingMa0]

Is your feature request related to a problem? Please describe.
I wish I could use cuml to obtain individual tree results of a random forest. However, this function is not supported in the current cuml package. Using the random forest regression function in the current cuml package, I can only obtain the average of tree results.

Describe the solution you'd like
An attribute in the existing random forest regression function to provide results from each tree.

Describe alternatives you've considered
I have been using the "estimator_" in the RandomForestRegressor function of scikit-learn to obtain individual tree ouputs, but that package only works on CPUs.

Additional context
https://scikit-learn.org/stable/modules/generated/sklearn.ensemble.RandomForestRegressor.html