var t,lit,i;

function tree(liter) {        

lit=liter;                      

i=1;                            

t = setInterval(show, 5);  

}

 

function show() {

var el;

if(el = document.getElementById(lit + i)) {

el.style.display = (el.style.display == 'block')?'none':'block';   

i++;       

}  

else clearInterval(t);       

}