Your pass code is a 4 digit number you need to unlock Moneytree when open the app. You will be asked to create one as soon as you register. You can choose any combination of 4 numbers for your Moneytree passcode.
You can see the request in the screenshot below.
"Please set a 4 digit pass code. You will be asked for this from now on when opening the application"
(Top:iOS version screenshot, Bottom: Android version screenshot)
If you see this message appear, make your 4 digit pass code and type it in twice. This number will be required when opening the application from that point on.
You can also set the app to unlock with Touch ID.
NOTE: If you fail to properly enter your passcode 4 times, you will be logged out of the app. You can reset your passcode when you login again.