int TREEisomorph(struct node *t1, struct node *t2){
    int i=1;
    if(t1==NULL || t2==NULL){
        if((t1==NULL && t2!=NULL)||(t1!=NULL && t2==NULL)) {
            return 0; // i due alberi non sono isomorfi
        }
        else if(t1==NULL && t2==NULL)
            return 1;
    }
    if(t1->val==t2->val){
       i=TREEisomorph(t1->left,t2->left);
       if(i==1){
       return(TREEisomorph(t1->right,t2->right));

       }

    }

    return 0;
}