\tikzset{level distance=15mm}
\tikzset{level 1/.style={sibling distance=85mm}}  
\tikzset{level 2/.style={sibling distance=60mm}}  
\tikzset{level 3/.style={sibling distance=12mm}}  
\tikzset{level 4/.style={sibling distance=12mm}}  

\node {tool}
  child[level distance=5mm] {node {manual}
    child[sibling distance=15mm, level distance=30mm] 
      {node[align=center] {text\\editor}}
    child[sibling distance=15mm, level distance=30mm]
      {node[align=center] {schematic\\editor}}
    child[sibling distance=15mm, level distance=30mm]
      {node[align=center] {layout\\editor}}
  }
  child[level distance=5mm] {node {automatic}
    child[level distance=15mm] {node[left=1mm] {analysis}
      child[sibling distance=11mm] {node {simulator}
        child[sibling distance=14mm] {node {analog}}
        child[sibling distance=14mm] {node {digital}}       
        child[sibling distance=18mm] {node {mixed-signal}}           
      }
      child[sibling distance=8mm] {node {DRC}}
      child[sibling distance=8mm] {node {LVS}}
      child[sibling distance=8mm] {node {STA}}
    }
    child[level distance=15mm] {node[left=10mm] {synthesis}
      child[sibling distance=15mm] {node[align=center] {PCell}}
      child[sibling distance=14mm] {node[align=center] {optimizer}}
      child[sibling distance=12mm] {node[align=center] {placer}}
      child[sibling distance=12mm] {node[align=center] {router}}
  }
};