regression_splitter.go

		// Recur down the left and right branches in parallel
		w := sync.WaitGroup{}
		recur := func(child **pb.TreeNode, e Examples) {
			w.Add(1)
			go func() {
				*child = c.generateTree(e, currentLevel+1)
				w.Done()
			}()
		}

		recur(&tree.Left, examples[bestSplit.index:])
		recur(&tree.Right, examples[:bestSplit.index])
		w.Wait()
		return tree