public BiTreeNode(BiTreeNode <T> left_child, BiTreeNode <T> right_child) : this(default(T), left_child, right_child)
{
}
public BiTreeNode(T val, BiTreeNode <T> left_child, BiTreeNode <T> right_child)
{
Data = val;
LeftChild = left_child;
RightChild = right_child;
}