code: @Override
  	public void clear() {
  		removeAllUserData();
  		if (this.children != null) {
  			N child;
  			for (int i = 0; i < this.children.length; ++i) {
  				child = this.children[i];
  				if (child != null) {
  					setChildAt(i, 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>.