Some software packages - or special add-ins for spreadsheets - draw decision trees automatically. Do a small survey to see what features these contain.
You can also draw a decision tree on a standard spreadsheet, as illustrated in Figure. This uses the DRAW options for drawing the skeleton of the tree, with calculations described in appropriate cells using normal spreadsheet functions. In particular, the MAX function identifies the best alternatives at a decision node and expected values are calculated as usual at random nodes. A useful tool here is the GOAL SEEK function, which you can use to find the probabilities needed to achieve a specific return. See how this works and explore the possibilities itoffers.

High sales 0.7 20 Optimistic 15.8 Sell 13.56 High sales 0.3 20 Pessimistic Market Market resear 10.2 10.2 0.7 Low sales 6 9 17.5 No market r High sales 17.5 Market Low sales 0.5 17.5 10 32