/// <summary>
/// function to count all features in this node and all child nodes
/// </summary>
/// <returns>The number of features in all this and all child nodes</returns>
public int CountAllFeatures()
{
var res = FeatureCount;
if (Nid < _tree.FirstLeafNodeId)
{
res += Child1.CountAllFeatures() + Child2.CountAllFeatures();
}
return(res);
}