rtemis internal: Recursive function to build Additive Tree
addTree(node = list(x = NULL, y = NULL, Fval = NULL, index = NULL, depth
= NULL, partlin = NULL, left = NULL, right = NULL, lin = NULL, part =
NULL, coef.c = NULL, terminal = NULL, type = NULL, rule = NULL),
coef.c = 0, max.depth = 7, minobsinnode = 2,
minobsinnode.lin = 5, learning.rate = 1, lambda = 0.01,
part.minsplit = 2, part.xval = 0, part.max.depth = 1,
part.cp = 0, .env = NULL, keep.x = FALSE, simplify = FALSE,
verbose = TRUE, trace = 0)