public static GbdtModel fromDom(Node doc) {
        Element dtree = XmlHelper.getSingleElement(doc, "DecisionTree");
        Element forest = XmlHelper.getSingleElement(dtree, "Forest");
        List<Element> trees = XmlHelper.getChildElements(forest, "Tree");
        if (trees.isEmpty()) {
            throw new IllegalArgumentException("Forest has no trees.");
        }
        List<TreeNode> model = new ArrayList<>();
        for (Node tree : trees) {
            if (XmlHelper.getChildElements(tree, null).isEmpty()) continue; // ignore
            model.add(TreeNode.fromDom(XmlHelper.getSingleElement(tree, null)));
        }
        return new GbdtModel(model);
    }
Return whether this model has sample information.
Don't bother to check every node as files either has this for all nodes or for none.
searchlib/src/main/java/com/yahoo/searchlib/gbdt/GbdtModel.java