void insert(int d) {
TN p = new TN(d);
if (root == null) root = p;
else {
TN nd = root, q = null;
while (nd != null) {
q = nd;
if (d < nd.val) nd = nd.left;
else nd = nd.right;
}
if (q.val > d) q.left = p;
if (q.val <= d) q.right = p;
}
}
