Java tree demo

package tree;

class TreeNode {
    int data;
    TreeNode left, right;

    public TreeNode(int d) {
        data = d;
        left = right = null;
    }
    public TreeNode(int d, TreeNode l, TreeNode r) {
        data = d;
        left = l;
        right = r;
    }
    public static void printTree(TreeNode node) {
        if (node != null) {
            printTree(node.left);
            System.out.println(node.data);
            printTree(node.right);
        }
    }
    public static TreeNode insertTree(TreeNode node, int d) {
        TreeNode last=null;
        while (node!=null) {
            last = node;
            if (d>node.data) node=node.right;
            else if (d<node.data) node=node.left;
            else return null;
        }
        TreeNode newnode = new TreeNode(d);
        if (last!=null) {
            if (d>last.data) last.right=newnode;
            else last.left = newnode;
        }
        return newnode;
    }
}
public class Main {
    public static void main(String[] args) {
        TreeNode root = new TreeNode(5);
        TreeNode.insertTree(root, 7);
        TreeNode.insertTree(root, -1);
        TreeNode.printTree(root);

        // TODO Auto-generated method stub

    }

}