Javascript XML Parser with same name of parent and child nodes

I am trying to parse a complex kind of xml with javascript and when I try to get the tag names.

This is the example XML:

<node:a>
     <node:a>value1</node:a>
     <node:a>value2</node:a>
     ....
     ....
     <node:a>valueN</node:a>
</node:a>

<node:a>
     <node:a>value1</node:a>
     <node:a>value2</node:a>
     ....
     ....
     <node:a>valueN</node:a>
</node:a>

......

......

<node:a>
     <node:a>value1</node:a>
     <node:a>value2</node:a>
     ....
     ....
     <node:a>valueN</node:a>
</node:a>

This is what I do:

xmlDoc.getElementsByTagName("node:a").length

It returns the length like this: All main tags with + All of the sub tags with

What I want is:

I want to get only the main tags (parent tags) and then I want to iterate over the parent tag one by one to get the child tags and their values.

Pardon me, if my question is too dumb.

Thanks