Classes and pointers in PHP

Hi, I'm quite new in PHP and i'm struglling with pointers and classes in PHP. I'd like to create a class with some information and 2 pointers ("next" and "down") to create a dynamic tree. The "next" pointer points to a new instance on the same level (level 0) and the down pointer points to an instance of the lower level (level 1) and so on. The instances should be put in the tree in the order that it was created. I tried to do it with recursive calls because every instance can have as many other instances again. Does anyone know an example of such a tree program or have any suggestion to do it in another way (for example with arrays)? Thanks in advance, Arnold