CREATE A DEPENDENT DYNAMIC DROP DOWN LISTS IN GOOGLE SPREADSHEETS

Hi, I would like to create a Dynamic dependent drop down list in Google docs. That means that I have 2 columns with different drop downlist: 1st Column 1 dropdown list with 30 categories (for example) 2nd Column 30 dropdown list with few subcategories each one When choosing a category from column one we need to see the dropdown list related to that category in column 2. We would like to have template that we can use always, where is easy to add and delete data. Thanks!