For general purpose graphical tree editing a tool like yED [1] might be the most flexible solution. yED's native GraphML can be easily transformed into other XML-like Structures.
If you like a plain text solution the TGF Format might suit your needs. It can also be visualized and edited in yED but it's very limited in its feature set.
A very nice and simple solution for visualization of small trees is to parse plain text with XSLT and transform it into SVG [2].
For are more programmable concept i would recommend to have a look at the combination of D3js [3] + JSON (or XML).
If you like a plain text solution the TGF Format might suit your needs. It can also be visualized and edited in yED but it's very limited in its feature set.
A very nice and simple solution for visualization of small trees is to parse plain text with XSLT and transform it into SVG [2].
For are more programmable concept i would recommend to have a look at the combination of D3js [3] + JSON (or XML).
[1] http://www.yworks.com/en/products_yed_about.html [2] http://www.xml.com/lpt/a/1472 [3] http://d3js.org