Class Products extends Component{ constructor(props)

{
super(props);
this.state={isLoadingCategory:false,
Categories:{}};

}
componentDidMount()
{
this.LoadCategories();
}
LoadCategories()
{
this.setState({isLoadingCategory:false});
api("GET", "warehouse", "get-category",{id_owner:1, isOpen:true})
.then((result)=>
{
this.setState({
isLoadingCategory:true,
Categories:result[0].children,
})
})
}
render()
{
console.log(this.state.Categories);
const {isLoadingCategory, Categories} = this.state;
return(<Container>
{isLoadingCategory && CategoryTree(Categories)}
</Container>);
}
}

const CategoryTree = (Categories) => {
return (<ul>
{Categories.map((Category, key)=>
<li key={key}>
{Category.children?
(<div>{Category.name}{CategoryTree(Category.children)}</div>):
(<div>{Category.name}</div>)}
{ProductTree(Category.id)}
</li>)}
</ul>);
}

const ProductTree = (id_category) => {
const [products, setProducts] = React.useState({});
return (<ul></ul>)
}

export default Products;

Ты хук в класс-компоненте объявляешь. Переписывай