The bartender is a billionaire.  They are distracted, counting wads of thousand-dollar bills.

The tree grows toward the bartender and shakes its leaves in the wind: "I grew here to purchase a beer, but take your time noticing me.  My grandchildren will be happy to buy a beer from you, too."

 The billionaire bartender glances at the tree, wondering when robotics will advance to the point that scattered trees can be harvested en masse for lumber.

The computer uses a turing machine to take robotic steps toward the bar at a linear rate.  When it reaches the bar in a finite time, it changes state, halts, and speaks: "I have exact money for a beer.  Give me one now."

 The billionaire bartender hires a team of professors to analyse the computer and discern how to profit from it.  The professors install analysis equipment in the computer, and record the beer exchange.

Team of Professors: "Here is your beer, computer."

Computer: "Here is your money."  The computer takes the beer and turns to the tree.

Computer to Tree: "It is now time to sit down while we drink our beers."

Tree to Computer: "I'm patient.  Let us grow on it and find the paths of sunlight and mast consumption in this environment."

 The computer looked for patterns in the expression of the tree.  It considered conditions for changing state.

Computer to Tree: "Purchase a beer now and sit with me at a table."

The professors reviewed their debugging logs and discovered that the computer was running wild, taking its commands from patterns demonstrated by a plant.