How to Add Node on Empty Tree

[fin-k]

Hi,

I know how to insert node to tree.

var lastNode = this.$refs.slVueTree.getLastNode();
this.$refs.slVueTree.insert(
      { 
        node: lastNode,
        placement: 'after'
      }
      , 
      { title: 'Node Test'}
);

But how can we insert node on empty tree? What object we must put on position params?