The 'onCheck' event only be triggered on the parent node. If you really want to make all children nodes to be triggered, please set the 'cascadeCheck' property to false and then call 'check' method on all children nodes.
$('#tt').tree({
cascadeCheck: false,
onCheck: function(node){
console.log(node.text)
var data = $(this).tree('getData',node.target);
if (data.children){
for(var i=0; i<data.children.length; i++){
$(this).tree(node.checked?'check':'uncheck', data.children[i].target);
}
}
}
})