How to anchor controls in WPF?

You can either set the HorizontalAlignment and VerticalAlignment on the TreeView or Button (I cannot tell which control you are trying to anchor), or you could place the control inside a DockPanel.

To space the control away from others use the Margin.

Margin="0 0 10 10"

will give you the margin only on the right and bottom

I hope this makes it a bit clearer:

<Window>   
  <DockPanel VerticalAlignment="Stretch">
    <TreeView DockPanel.Dock="Top" />
    <Button DockPanel.Dock="Bottom" Margin="0 0 10 10" />   
  </DockPanel>
</Window>