code: @Override
  	public void clear() {
  		super.clear();
  		if (this.nicosep != null) {
  			final N child = this.nicosep;
  			setIcosepChild(null);
  			child.clear();
  		}
  	}
docs: Clear the tree.
  
  <p>Caution: this method also destroyes the
  links between the child nodes inside the tree.
  If you want to unlink the first-level
  child node with
  this node but leave the rest of the tree
  unchanged, please call <code>setChildAt(i,null)</code>.