I use Tree Importer to draw diagram from database and then I use a NTextShape for writing header title in my document. But the diagram covers my TextShape because it's in front of it. How can I move down my Tree so I can see the title into TextShape?

By default layouts arrange the drawing relatively to the upper-left corner of the drawing.Bounds. That is why the tree/graph data importers arrange the drawing at the 0,0 origin. - provided that you have not modified the drawing.Bounds . The easiest way to place a header on top of your arranged drawing:
1. Import the data first,
2. Add the header text shape on top of the drawing.Bounds rectangle (for example with bounds new NRectangleF(0, -20, 1000, 20)).
3. Call the document.SizeToContent() method.

Best Regards,
Nevron Support Team