There wasn't much point in sneaking a gift under the tree with Sherlock around the house, but old habits die hard, so early Christmas morning John crept out of bed, trying not to shake the mattress. Sherlock groaned but rolled over and went back to sleep immediately, much to John's relief. The doctor padded down the hall, trying to avoid the squeaking floorboards as he went. Sherlock slept fitfully at the best of times; making too much noise would surely rouse him from sleep altogether and ruin the surprise.
Being careful to dodge around Sherlock's varying experiments –why that man couldn't keep them contained to the upstairs bedroom, John would never know, it's not as if John was actually sleeping there- John approached the tree in its corner of the living room. They'd left the fairy lights on at Sherlock's behest; John still thought they looked like a fire hazard, but so was just about everything else in the flat, so the point was moot. The lights reflected off the ornaments, making strange shimmering shadows on the walls while John tried to find the best spot to place his gift. His parents had always hidden his first gift, making it a sort of challenge to find it before the presents could be opened. He knew Sherlock would enjoy deducing the gift's hiding place just as much as he'd enjoy deducing the gift.
Finally the perfect hiding spot presented itself. Tucked behind the pile of papers stabbed into the mantelpiece, so that the skull and knife hid it from view. Obscured enough to be missed on first inspection but quick enough that Sherlock would find it merely amusing.
John gave a last look around the living room, trying to see if he'd left any tracks. He couldn't discern any, which meant any he'd left were subtle enough only Sherlock would see it. The room looked like home, despite the strange sounds coming from Sherlock's gurgling experiments, or possibly because of them. It wouldn't be home without the threat of an explosion, John thought wryly as he slid back into bed.
Sherlock immediately noticed his presence, curling up to his doctor instinctively, seeking out the new source of warmth in the bed. John smiled, sliding an arm around Sherlock and drawing him closer. He hadn't realized how cold the rest of the flat was until he was back in bed, wrapped in the warmth of the multiple quilts Sherlock insisted on having. John fell asleep quickly, happily waiting for the morning when Sherlock would go to search for his gift.
Once he was certain John was asleep, Sherlock extricated himself from the embrace and slid out of bed. John had woken him up the moment he'd left bed, but Sherlock had allowed John to creep about, knowing it'd make him happy. Now, though, John was sound asleep and Sherlock was free to put his gift for the doctor under the tree.
Much faster than John had managed, Sherlock navigated down the hall and into the living room. He remembered where everything had been left and so didn't have to give pause after each step to determine where he next would step. Sherlock quickly concealed the package inside the tree's branches, ignoring the small pricks and sticks of the needles as he did so. Once the gift was properly concealed Sherlock was tempted to search and deduce his own present, but decided John would probably be annoyed with him if he acted on the idea. Instead he joined John back in bed and burrowed deep in the quilts to wait for morning.