Hi, can you explain this error for me?

Blockquote

///////////////////////////////

In my A.h file:
struct TreeNode;
struct TreeHead;
typedef struct TreeNode * Node;
typedef struct TreeHead * Head;

///////////////////////////////
In my A.c file:
struct TreeNode {
    char* theData;
    Node Left;
    Node Right;
} ;

struct TreeHead{
    int counter;
    char type;
    Node Root;
};

Head Initialisation() {
    Head treeHead;
    treeHead = malloc(sizeof (struct TreeHead));
    treeHead->Root = malloc(sizeof (struct TreeNode));
    return treeHead;
}
///////////////////////////////

In my Main.c file:
    Head head;
    Node tree;
    int choose =5;
    head = Initialisation(); 
    (head->Root) = tree; //When compiling, this line has an error: error: dereferencing pointer to incomplete type

Blockquote

haed->Root will return a Node pointer, tree is also a Node pointer. So why error is dereferencing pointer to "incomplete" type?