Simple BST with no copy & paste

bst.c

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <stdbool.h>

typedef enum eChildKind {
    LEFT,
    RIGHT,
} ChildKind;

typedef struct tTreeNode {
    struct tTreeNode *children[2];
    int data;
} TreeNode;

typedef struct tTree {
    TreeNode *root;
} Tree;

TreeNode **child_of(TreeNode *parent, ChildKind kind) {
    return &parent->children[kind];
}

Tree *create() {
    Tree *tree = malloc(sizeof(Tree));
    if (tree == NULL) {
        return NULL;
    }
    tree->root = NULL;
    return tree;
}

TreeNode **find_place(TreeNode **node, int value) {
    if ((*node == NULL) || ((*node)->data == value)) {
        return node;
    } else {
        ChildKind kind = (value < (*node)->data) ? LEFT : RIGHT;
        TreeNode **child = child_of(*node, kind);
        return find_place(child, value);
    }
}

bool contains(Tree *tree, int value) {
    return *find_place(&tree->root, value) != NULL;
}

void add(Tree *tree, int value) {
    TreeNode **node = find_place(&tree->root, value);
    if (*node == NULL) {
        TreeNode *new_node = malloc(sizeof(TreeNode));
        assert(new_node != NULL);
        for (ChildKind kind = LEFT; kind <= RIGHT; kind++) {
            *child_of(new_node, kind) = NULL;
        }
        new_node->data = value;
        *node = new_node;
    } else {
        assert((*node)->data == value);
    }
}

void print_impl(TreeNode *node, int depth) {
    if (node != NULL) {
        for (ChildKind kind = LEFT; kind <= RIGHT; kind++) {
            print_impl(*child_of(node, kind), depth + 1);
            if (kind == LEFT) {
                // it's a binary crunch
                for (int i = 0; i < depth; i++) {
                    printf("  ");
                }
                printf("%d\n", node->data);
            }
        }
    }
}

void print(Tree *tree) {
    print_impl(tree->root, 0);
}

int main() {
    Tree *tree = create();
    add(tree, 5);
    add(tree, 3);
    add(tree, 7);
    add(tree, 1);
    add(tree, 4);
    add(tree, 6);
    add(tree, 8);
    add(tree, 5);
    add(tree, 8);
    print(tree);
    for (int i = 1; i <= 9; i++) {
        printf("%d: %s\n", i, contains(tree, i) ? "yes" : "no");
    }
    return 0;
}