We tried a "Caught you being good jar" system. It is similar to your kindness tree (I like that idea!). Every time we "caught" the kids doing something good they got a Hershey kiss to put in their jar. When they did a chore, they got a kiss. When they shared something of their they got a kiss. Sometimes they could earn bonus kisses for various things. When the jar is full they get to pick something special. For our kids, it was a small toy, but it could be whatever you set up ahead of time for them. Then they start filling the jar up all over again.
It requires a lot of work on your part at first. You want to reward them for all the little things and get them in those habits you are hoping for.
Best of luck to you!!