Its not illegal as long as your friend trusted you so much and you will commit on that. But hey, dont spoon feed your friend because its not healthy to do so, let him know the market of cryptocurrency so no one can blame for if he incur losses because in the first place you guide him to start his journey here and the rest would be depend on his goal.
giving help to friends may be better, than we make a purchase for someone else, because the potential loss that we can get is unknown to our friends, this can create a bad problem, we must open ourselves up in trading, always provide assistance in bitcoin trading maybe safer, profit and loss, we will always be detected.