Real trees are wonderful, but it is not always possible to put them exactly where you want them. You can plant one, of course, but it will take years for it to become the majestic giant of the forest you crave. If you have need of a large tree in a place trees are not ordinarily known to grow---inside your house for example---and you really want it now, build a ferro-cement fake tree instead.
Find a real tree with a bark pattern you like. Gently brush all loose bark, debris and dirt away with a soft brush. Get permission if tree is not yours.
Apply coat of liquid latex over several different sections measuring roughly one foot square or larger each. Allow it to cure; repeat until a pad of rubber ¼ inch thick is achieved.
Remove textured pads by pulling back edges and gently "rolling" them off the trunk---damaging the tree as little as possible. Dust with cornstarch or talc and set aside for later use.
Measure and cut four plywood disks the same size as the interior diameter of your Sonotube. Screw together two (each) of the disks to form pairs of double thickness disks---label A and B.
Attach disk A to a large scrap of plywood with 1-1/2 inch deck screws fastened from below to form a base. You may need to weight base to prevent tipping when you apply concrete to the tube.
Place disk B inside the upper end of the Sonotube and secure in place with 1-1/2 inch deck screws. Stand Sonotube upright over the disk A on the base and fasten it as with B.
Wrap the Sonotube tightly with at least two layers of chicken wire secured in place with heavy staples in several places. Alternatively tie baling wire to chicken wire and Sonotube through pre-drilled holes.
Follow package directions to mix only as much cement as you can handle before it cures. Apply "scratch coat" to chicken wire with a trowel, pressing firmly to ensure good contact and leaving a slightly roughened surface with some wire still exposed.
Wrap trunk in damp burlap or old towels---allow it to harden for 24 hours.
Mix and apply a second coat of cement as before, but---working one small area at a time---use rubber texture pads created in step two to press a bark pattern into the wet cement. Overlap and rearrange pads to avoid a stamped, unnatural look.
Leave trunk unwrapped until firm enough to withstand moderate pressure without disturbing the pattern---keeping damp with a hand mister. Re-wrap with damp cloths once it achieves sufficient hardness and let cure at least three days.
Stain or paint your fake tree using materials specifically designed for concrete. Remove temporary base and secure on location as appropriate.
If your fake tree is to be temporary, or you want to cover an unsightly pole or other object already in place, build your "tree" in two parts---placing hook and eye latches in the separate halves so you can attach or remove it easily. Create limbs for your tree by wiring smaller tubes to the "trunk" prior to applying cement. You can also give your trunk a natural, grounded appearance by shaping wire into buttresses at the base before cementing. For an extra bit of reality, mix coarsely crumbled eggshells or perlite into thick grey, pale blue and sage green paint--daub on trunk to simulate lichens. Spanish moss draped from branches makes another touch of realism.
Wear gloves and use eye protection when applying cement. It is very caustic and may cause burns.