Linker error - Undefined reference to 'Node::~Node()'

[C++]

I'm trying to set up a couple classes, but I'm getting an error: Linker error - Undefined reference to 'Node::~Node()'. I think it might have something to do with how my headers are set up, but I'm unsure what I need to do to fix it. (FYI I added using std to try to fix some other problems,...