程序代码：

#include<stdio.h>
#include<stdlib.h>
typedef struct tree tree;

struct tree
{
    int data;
    tree *left;
    tree *right;
};

tree *tree_add(tree *root,int num)
{
    if(root == NULL)
    {
        root=malloc(sizeof(tree));
        root->data = num;
        root->left = root->right = NULL;
        return root;
    }
    else if(root->data < num)       

        root->right = tree_add(root->right,num);
    else if(root->data > num)
        root->left = tree_add(root->left,num);
    else
        return root;
}

int print_tree(tree *p)
{
    if(p->left != NULL)
        print_tree(p->left);
    printf("%d\n",p->data);
    if(p->right != NULL)
        print_tree(p->right);
}

int main()
{
    tree *root;
    int num[10]={5,0,4,7,8,3,2,1,6};
    for(int i=0;i<10;i++)
        if(root == NULL)
            root=tree_add(root,num[i]);
        else

            tree_add(root,num[i]);
    print_tree(root);
}