This was a series of children's books, originally written in the 1940s by Enid Blyton, but still going strong decades later.
Three children - Bessie, Joe and Fanny (sometimes joined by other children, like their cousin Dick, and the spoilt Connie) - moved to the country and discovered a tree, populated by magical creatures. The tree grew all kinds of fruit and nuts. At the top of the tree, they climbed through into different lands - they rotated, so there was a different one every time, such as the Land of Take What You Want; Do As You Please; Topsy Turvey Land; the Land of Goodies; Teaparties; Treats; Spells, etc. There were also strange but delicious sounding foods, like Pop Biscuits (which popped in your mouth and were full of honey), Toffee Shocks (which got bigger until they finally exploded), and Google Buns (a cross between a currant bun and a sherbet lemon). To get down from the tree, they slid down a long slide called the Slippery Slip.