Willow as a plant/tree means in german "Linde" / "Lindenbaum". http://en.wikipedia.org/wiki/Willow http://de.wikipedia.org/wiki/Linden_%28Botanik%29 There is a first name "Linda". http://en.wikipedia.org/wiki/Linda_%28name%29 Therefore why don't you call yourself Linda?

Wilma, Werna, Emma, Mia, Lena, Lara, Lisa, Julia, Jule, Ida, Ina, Katrin, Katharina, Sophie , Sophia, Maja, Tanja, Tina, Caroline, Theresa, Lea, Lina, Annika, Anna, Anja, Marie, Sina, Luisa.. There are lots of possible names, which also fits internationaly / are also used international. I think short and more traditional names are popular. :) Maybe you should just choose a name you like and ask if it sounds weird or too oldfashioned, :)

If you want to stay with trees maybe Linde (not Linda - Linda is a famous potato variety in Germany and sounds as a girl's name English not German) or Birke. If you want to stay with the Wi-sound maybe Wibke (really northern) or Wini(-fred) for true Wagnerians. The only Names close to Wi start with Ve like Veronika, Vera, etc.