My brother and I have been searching for a picture book that we were particularly fond of as children. I don’t remember the title but it would have been published in the late 60’s or early 70’s. The story is about a boy (possibly named Keith) who has his father help him built a fort in a large tree in his back yard. Some neighbor children come by to play, and they end up adding their own structures to the tree. I remember one of the friends puts a big wash tub up in the tree and pretends to be an astronaut in a ship. Some girls bring their dolls up in the tree and make a tent with a blanket or some kind of hammock. There’s also a plank that they stand on that is supposed to be a raft? Maybe one of the kids was a pirate? Not sure, but before you know it, all the neighborhood children are playing in the tree. I can still see the illustrations in my mind’s eye and and would recognize it if I saw it. Thanks!