How Do I Loop Through A SiteMap To Build A Recursive String

Say for example I have a sitemap like so (with varying levels).
Node 1 Node 1.1 Node 1.2 Node 2 Node 3 Node 3.1 Node 3.2 Node 3.2.1 Node 3.2.2 Node 3.3 I want to populate a dropdownlist with results that would look like so.
Node 1.1 : Node 1.1 Node 1.1 : Node 1.2 Node 2 Node 3 : Node 3.1 Node 3 : Node 3.2 : Node 3.2.1 Node 3 : Node 3.2 : Node 3.2.2 Node 3 : Node 3.3 Nodes with children (e.g. Node 1, Node 3, Node 3,2) have no url and are only for hierarchical organization so they should not have their own item in dropdownlist.
The best output results i have been able to get so far is: Node 3.2 : Node 3.2.1, but it was mis ...